My air conditioner gets warmer when pulling our fifth wheel. it only does it when pulling and we keep having to turn it up to 3 & 4 to stay cool. anyone know what causes this or is this normal. Thanks Steve

Could be heat load, all that extra heat from towing reduces the ability of the system to scavenge heat from the cab. Traveling in 100*+ on real hot days will cut my AC efficiency, it still cools but not as cold.

In an unrelated incident, my 2006 had a micro-leak in the condenser that dropped the refrigerant pressure. Took the dealer four days of searching to find even with florescent dye in the system. Wife and I heard a faint sound like a phone ringing in the glove box that came and went. It was the AC compressor cycling on and off more frequently. If you are worried about it, have the dealer or an AC shop check the refrigerant level. Low level can damage the compressor. Your symptom could still signal a need for servicing. AC does need periodic checks and service.

When towing, the engine RPMs run higher, and a system with a low charge will shut off the compressor more often with the higher RPMs. The system is designed to cutout the compressor when the suction side drops below 28psi, give or take.
Also, blockage in the cooling stack will yield a similar complaint.