1983 C10 305 mind boggling engine problem

[thomps92]

Hello, This is my first post. I am at my wits end. I have a 1983 C10 with 100,000 miles on it. For the last few months the truck has run like a piece of garbage. The main symptoms are that it starts seemingly well, but I will drive it for about 10-30 miles and then all of a sudden the engine will bog down, it won't downshift softly and then the engine temp gauge starts to rise to about 210-230 degress. Sometimes the problem goes away and other times it won't. But all the while the engine has very little power and wont accelerate even with the pedal on the floor. Most of the time during these episodes when depressing gas pedal fully the engine will spit and sputter and have very little accelerating power. Just installed new cap and rotor which made it idle alot better and initially helped truck respond better, but the main problem still exists with the bogging/shifting/overheating problem after 10-30 miles. temp gauge reads normal up to this point. I am thinking I should replace the entire distributor, but want to rule out other problems. There are no vacuum leaks. Any ideas? Thanks guys.