I recently bought an '89 GMC 3500 - 454. Has 64,000 original miles. I bought it to tow a light weight 20' travel trailer with plans to ultimately be able to upgrade to a larger trailer or a camper/boat. Towed with it for the first time this weekend and the truck had NO power, but more concerning was how hot it got - operated in the 220-230 range on the flats and climed up to 240+ on the hills. I could NOT run the AC and had to run the heater the whole time. I put in a 180 degree t-stat before towing. I had high hopes that going from a Dodge with a 5.9 liter to a GM with a 454 would allow me to tow a larger trailer, or at least tow my little trailer with ease. I'm not very knowledgable with diagnostics but can turn a wrench and find components. Any idears about what to start with? Cooling system flush? fuel filters? Air filter? water pump? new radiator? Any help is appreciated.