I went through that exact thing with Furd in 2003. We bought a 2003 Furd F250 crew cab short bed diesel, then with Furd's tow guid in hand, we went trailer shopping. Found our trailer that was under the weight Furd's tow guide said the truck would handle. Picked the trailer up on a Friday evening and returned to the RV dealer on Saturday. The combined rig nearly beat us to a pulp on or way home. RV dealer kept the combined rig for close to a week and put over 100 miles on it checking and trying various things to smooth out the ride. RV dealer offered our money back on the trailer but assured us the problem had to be with the truck since they had sold the identical trailer to a lot of folks driving the same model truck.
Since that model trailer was the only model they stocked that had a bedroom head height I could stand up in, I talked to the Furd dealer first. Furd sent an engineer from Kansas City to check it out. He couldn't find anything obvious, but after driving the rig agreed there was a problem. He went back with a copy of my scale tickets that confirmed that my trailer was well under the tow guide limits. Also, my axle weights for the truck were under their individual limits.
About a week later, I got a phone call from the Furd zone manager. He congratulated me for having a problem that had generated the longest chain of internal email he had ever seen. When I asked for a copy, the red flags went up. "COMPANY CONFIDENTIAL" was the reply. Bottom line, according to him, was that I had bought the wrong truck! Even though I was well under on all individual weights, when the two truck axle weights were added, I was over the GVWR of the truck by 500lbs. Suddenly, it was no longer Furd's problem, even though all my trailer weights were well below the tow guide limits. The zone manager tried to explain that my pin weight was the problem, even though the tow guide stated that the pin weight MUST be between 15% and 25% of the gross trailer weight. Mine was 20%.
Bottom line is that I now drive a 3500 Chevy CCLB diesel because Furd offered less than average trade value for my 4 month old, 4500 mile F350, even though I was told they were including an additional $2,000 on the trade because of my problems. Chevy dealer beat the offer and did so without owing me any good will. Sour grapes?? You bet!