To OP, All respondents have given great advice and if you read these guys posts as much as i do, you know they are speaking from hard won experience.
First off, I have a long bed, extended cab 3/4 ton, gas Chevy with 6 spd auto. Its geared 3.73:1 and I run LT 'E' rated tires on 18 inch rims. I carry a 94 model Lance 480 that weighs roughly 3600 pounds ready to camp. The lance is a non slide, aluminum sided, aluminum roof deluxe camper. Its 9.5 ft. Long. My truck weighs about 7000 pounds gassed up and gets about 16.5 mpg unloaded on a steady 70 mph cruise and about 12 mpg with the camper. It has plenty of power to cross Colorados numerous high passes.
I don't pull a trailer and my only suspension mod are Torklift International stableloads. The truck rides about 1 inch high in the rear and I want to put a rear sway bar on. It needs it.
I camp with my wife and 3 dogs. 2 small dogs. One lab.
We do well with the space.
Now, all that said. If i had a heavier camper, i would not be comfortable without making more mods or buy a higher capacity truck. I personally don't desire or feel a need for diesel power.
I hope this helps. I'm sure we all want you to be happy with the results of your decision.
Best of luck! DT.