I've seen full sized pickups towed behind motorhomes of varying lengths, so yes it can be done. I'm not sure exactly what you are asking. If you're asking can your motorhome tow your full size pickup, I think you've already answered your own question. According to your posts, you will be grossly over weight and therefore not legal. Could you "get away with it"? Possibly. I just watched a YouTube video of an electric F150 towing a "1 million" pound train. It didn't try to stop it and it was on rails, it also didn't try to tow it up a hill. I'm not the "weight" police so often referred to, but I would say use common sense (is there such a thing anymore?).
There are motorhomes that are properly equipped to tow that much weight. I don't believe most 90's model RVs, especially gas chassis models, are though. There was a major shift in RV chassis design in the early 2000's to address significantly under rated chassis of previous models. The workhorse chassis had significantly higher weight capacity than the P-series GM based models. I didn't keep up with the Ford chassis, but I'm pretty sure almost all of the 90's models weren't up to the task of hauling the coaches built on them. Maybe others have a different experience or more insight into Ford chassis. Again, my experience lies with the GM based chassis. My BIL had a 90's P-Series chassis Bounder. When we bought the 2004 Bounder on the Workhorse chassis, he drove it and the first time he stopped he nearly threw us all through the windshield. His comment was "wow yours has brakes".