2005 2WD 2500 Ram Crew Cab HD SLT SB Automatic Cummins

Can't help with what sort of 5ver. Anything under 12-14000lbs is a good match though in general.
Couple things about the truck, if it's in good shape and you're planning on keeping it for a long time.
1. Ditch the OE 17" wheels. You can find OE 18" or 20" takeoff wheels and tires cheap and they will have more available tore capacity and choices.
2. Stock 3rd gems leave a little to be desired in the power department when towing gets heavy. With a stock trans you can do a mild tow tune that won't destroy the trans. 30-40hp and 60-80 ft lbs bump in power. If you are serious about making th ole 05 a real towing beast then a built trans is in order and you can bump up 100hp or more easily.
3. Exhaust brakes are worth the $ IMO. I'd doo this first before any other mods.
4. The above 3 mods are the only things you would need to do to make that truck hang with a brnad new one up and down the Mountain. But you're looking at about $7k min to accomplish that. 3k or so for the exh brake, programmer and some new wheelz would get you mostly there except in the power department. The rest of the truck is already built to handle whatever you can throw at it.

Last thing, how many miles, how many miles on injectors, and do you have additional fuel filtration? That is the most important thing to look into IMO on 3rd gens.
A lot of owners, myself included only get 100-150k on OE injectors without additional fuel filter. OE filter is not up to par. 2micron add on kit is $200 if you buy one manufactured, or about $50-100 if you make one. Either is worth it....today.

Thanks for the replies so far. I have more question about towing, and maybe some modification (if possible) but 'first' what sort of 5th wheel should we be looking at that will safely and easily meet my towing abilities. We're not looking for a monster 5th wheeler. Just looking for some suggestions on 'specific brands/models etc., so we can check Craigslist, visit a few dealers and narrow down our options. Who knows we may got another route and buy a Class C or something.

Thanks for your time ...

I have the same truck except 2004.5 and a dually. I tow a 10k# fifth wheel and it does fine. The numbers I have limit the truck to about a 13,000# fifth wheel. The engine is capable enough but has a tendency to generate high exhaust gas temperatures on grades which is my limiter, not power. The transmission isn't perfect and I find my sweet spot for towing to be 62-65 mph in OD. Tow haul for any grade work. An exhaust brake is a must have. My original window sticker showed the axle ratio (3.73) if yours is still available. My truck weighs around 7,200# empty GCWR is 21,000#.

I am pleased with our truck and feel it makes a nice combo with our trailer. I have owned it for 5 years and it has always delivered us without drama or incident. I would have no problem hooking it up right now and head across country.

"(Folks are going to flame me....but GVWR is for MFG Class Rating/Warranty and Registration purposes....NOT a 'Legal' issue. Axle/tire ratings are)"

YES! Licensing and Insurance purposes. Rear tires will be the limiting factor.

Same with my 15 RAM DRW 14k GVWR. I am at well over 15K on the 6 tires but loading the rear axle to it's SAE RAWR and adding NOTHING to my front I am at 15K. It's smoke and mirrors. I am licensed to carry what ever weight I am with SD licensing.

That 5.9L CUMMINS is great motor
Rear Diff 3:73 gearing
Trucks RAWR is 6010#
Truck rear tires are 3195#/each at 80 psi

With only 9000# GVWR you will easily exceed that rating
But stay under/at RAWR and you will be just fine
(Folks are going to flame me....but GVWR is for MFG Class Rating/Warranty and Registration purposes....NOT a 'Legal' issue. Axle/tire ratings are)

GVWR 12K 5vr with a wet pin of 2650# (22%) would be a good match for truck


VIN Decoder

It will easily handle a 12k GVWR 5er