Buying advice? 2012 Ram 3500HO vs 2013 Ram 2500 Longhorn vs 2015 Ram 2500 Longhorn

Did you upgrade your T. Or are you still looking?

You have a older 2500 truck so you may know how it pulls the trailer. 

 My '03 2500 Dodge/Cummins 305 hp/555 torque HO NV5600 tranny pull my 11800 gvwr 5th wheel trailer with ease. Any of those three have better capacities  and will have no issues with that size trailer. 

 Agree run away from a deleted diesel pickup. Not worth the cost if you get caught.

Well back again, if looking at Rams, look for 3500 if planing on towing a 5th wheel. 
look at at least a 2013 or newer as GVWR took a big jump in 2013.

if budget allows look 2015 or newer as they went back a single radiator.

Something to consider is how far to look, when we were looking used the selection locally was a little thin. I went to  Car gurus and set distance at 500 miles. We ended up traveling over 250 miles to get our truck.

I would be looking for a '18 truck and stay away from a emissions deleted truck.

Well I would skip both #2, and #3 as not enough truck for a fifth wheel. I would be concerned about #1 due to the need for new ball joints before 100k miles.

Keep looking.

Not much tech info on those trucks for any advise example; gas or diesel....2wd or 4wd....  bed size...cab types.....tranny types... wheel base/etc.

From my armchair knowing absolutely zero about the trucks other than year and mileage - No 3. But if it was me, dollar for dollar, I’d be looking for newer trucks with less mileage rather than old truck with more luxury. I’d pull out all the stops to buy a newer truck. YOMV