My MIL has a 2500 (same thing, just 1/2 ton vs. 3/4 ton I think) and I can't fit my son's Evenflo Triumph rearfacing outboard b/c it runs into the back of the front seat and I can't get the right incline. I can get it in the center though since it can poke up between the front seats. I would imagine it would be worse with a Wizard or a Marathon. I really wanted to get a new Quad Cab this summer, but I won't be able to until ds#2 is FF since his seat can't fit outboard and ds (and I use that term loosely lol)#1 pokes at his little brother if they are sitting next to each other. FF'ing seats fit perfect though. I have had the Triumph, a FPSE and an Evenflo Chase in there and they all were solid as a rock. I've also had various RF infant seats fit great, it's just when you try to use a convertable seat that you have problems. If you can put a RF'ing seat in the center, it's fine though.
Hope that answered your question. I'm really bummed b/c I was looking forward to finally having a new truck and new car seats (I'm getting a Wizard next week), but now I have to rethink my plan so ds#2 can stay RF'ing for a while longer.