1990 Chevy C1500 runs bad when warmed up?

Seth: Would it be worth it to get an independent diagnosis with technicians trained to work on your make year model GM vehicle? Do you think your better than the company that designed the vehicle and has the test equipment and technicians to work on it? I say spend $100 to have the vehicle diagnosed by your GM dealer. They will hook up their GM OBD-II scanner and give you their opinion as to how it's running. It could be worth the $100 to have a fresh set of eyes and ears looking at the truck.