installing hitch in 2003 GMC 2500HD 8 foot box(updated)

I cannot understand how this happened if you used the metal shims recommended. The purpose of the shims is to avoid this.
Never happened to me when using shims. Sorry for your experience!

Nope all hand tightened, followed instructions with kit they sold me, in fact here is what they say if rail only sits on one rib of pickup box.

Shim will be used to support the rail. Place shim
between ribs of pickup box and center front to back of rail.

But in talking with them my rail in the bed spans two ribs and sit flat and does not tip at all, my problem is the underneath, my two fords had no issue, and my last GMC that the hitch came out of never had an issue either, so not sure what to think, but looks like a shim of some sort up top in box would have worked.
But according to the instructions am my talking to Demco I should not have an issue.
Here is what he said in one e-mail.


Sorry to hear about the difficulty in the installation. I haven't heard that this install on a 2003 GMC has been a problem. I'm assuming you are using hole #1, #3 & #5 on the rail.
Does your frame look different than the one pictured in the instruction?

partsman01 wrote:
Okay, have always installed my own hitches, now have to transfer hijacker 24sl hitch to this 2003 GMC with the long box, 4X4,.
looks like the frame should be alright to get at to drill, but wondering if there are any issues to look out for, like the back I can see the frame is open, but up further it is hard to see and not sure if I need the fishing wire that came with the install kit.
I had to buy a new kit because my old 96 kit was not compatible, and also the instructions show the bolts going in from inside the frame to the outside and then nut and washer are on the outside, and I see these bolts are knurled, so guess one should not use an impact to install, anybody done one before?

partsman01 wrote:
Well been a bit of a nightmare, once I started drilling the holes found out the bolts in the middle bracket would be too close to a raised part of the frame, so bolts would not sit flat, had to drill further over towards the back of the frame, front ones on left side are by the fuel tank, so turns out there is a bracket in there and can not even get the bolts supplied to fit in the space, cut them to 1 1/2 still too long to go in, so will have to try put one in from outside in, but even though I set hitch like they said to at 24 1/2 inches from back of box it did not turn out well, and then tonight while torquing the only bolts I can get a torque wrench on after cutting three holes in the heat shield on the left side, turns out the bracket as it got tightened crushed the box floor up to the rail above, no where in the kit was there any spacers, and supposedly not needed, but it appears they were needed, but done now.
Not too happy with they way it turned out.

Well seeing how it came with instructions, did your read and follow them?? They specific areas by year and model.

I would NEVER use an impact wrench to install a hitch, all of the fasteners have torque specs, that is what you tighten to. With a impact wrench you can easily over torque a nut and bolt combination, and compromise the strength of the bolt. My impact wrench can remove a bolt tightened to over 220#!

All kits I have ever gotten, had spacers for the ribs in the bed so you don't crush the bed.

It looks like you have already done the install your way, if you did use a impact wrench for the install, I would get all new fasteners and use a torque wrench as you have likely compromised the existing fasteners.

Well am not impressed with this set up.
Would not expect it to crush the box.

Installed my B&W in my 03 GMC. Near as I can't remember only had to drill one hole. However, it was a biggy. A 4 incher in the middle of the bed. Only took a couple of minutes.

Well been a bit of a nightmare, once I started drilling the holes found out the bolts in the middle bracket would be too close to a raised part of the frame, so bolts would not sit flat, had to drill further over towards the back of the frame, front ones on left side are by the fuel tank, so turns out there is a bracket in there and can not even get the bolts supplied to fit in the space, cut them to 1 1/2 still too long to go in, so will have to try put one in from outside in, but even though I set hitch like they said to at 24 1/2 inches from back of box it did not turn out well, and then tonight while torquing the only bolts I can get a torque wrench on after cutting three holes in the heat shield on the left side, turns out the bracket as it got tightened crushed the box floor up to the rail above, no where in the kit was there any spacers, and supposedly not needed, but it appears they were needed, but done now.
Not too happy with they way it turned out.

Well almost got my install done today, but ran out of time, here it is so far.

Thanks for the replies, I will have to check it out, as the regular 2500 shows drilling through both frames and using 4" bolts, but this kit and instructions for mine show only the 1 1/2" bolts and not drilling through both sides of frame, only one side which leads me to believe it is an open frame in both places, the only other thing because of those bolts having serations that is why they have to go through from inside frame, and not through brackets first I gather.

Relatively easy install. You will need the fishing wires to pull the bolts through the frame. Make sure you use the listed 17/32 drill bit. that is key in getting the bolts to grip the hole in the frame when you tighten them up.
I have also used the no drill kits that clamp to the frame. They also work well.
Be aware of wires and brake lines on the drivers side when drilling the frame rails.

Did my own install on my '06 and '11 Silverado's. Best advise I recieved was to use the installation kit available thru eTrailer. The frame brackets made the job pretty easy.