My buddy has a GMC extra-cab shortbed, with a 6" lift and big tires. He uses regular ramps he bought at the dealer and loads two Z400's in the back. Has to stand the front one straight up and noses the other one right up to it. Doesn't have to rest on the cab at all. Uses ratchet straps to secure it, works really well. He doesn't have any problem riding them up the ramps into the bed. It is a little steep, but no problems.
I have a 99.5 F-350 4x4. It sits rather high in stock form due to the 4" factory blocks on the back. I ended up going with 8' OxLite ramps. Look Here
The ones I have are PN 13492. Tractor Supply has them for like $139.
I tried 6 footers but did not care for the angle. Looks OK from the side, but feels like straight up when you are loading.
I'm in the same boat. I've got a 2002 Z71 that I lifted 9" and running 36" super swampers and it's a PITA to get my Kodiak in it. I have to back up to a berm, wall, or hill. Anything to make the angle less steep.
Never checked on the new Ram's, but on my old 84 F-150 I would un-hook the tail-gate cables and let the tailgate drop some....That always sem to help with the angle a little bit.....just make sure the ramps are secure. I have an eye bolt on the bottom of both ramps and use the tie down straps hooked to them and to the bumper to hold everything nice and tight.