I tow with a 1/2 ton ford with a 6 1/2 foot bed with no issues, and I don't have a slider hitch, but mine is a club cab not a 4 door. You have to be careful when backing up into tight areas as if you get jack knifed the trailer can hit the cab of the truck. They make slider hitches for this purpose, BTW it has nothing to do with 1/2 ton or 3/4 ton but the bed length is the critical part.
Every truck is a little different and so are every 5th wheel, many are changing the kingpin location and rounding the corners of 5th wheels to accommodate the newer 4 door trucks with shorter beds....
My trailer is very small and I have not come even close to hitting the cab and have backed up pretty sharp turns with no issues, you just need to try it and be aware of the problem and don't get yourself in a position you have to turn tight while backing up...I try and avoid that anyway.
Keep trying, it will work but with a 1/2 truck you can't haul a very big 5th wheel, no matter what the dealer tells you, check it out carefully.
I am right now shopping for a bigger truck and ultimately a slightly bigger 5th wheel.
Good Luck,
Jim