Hello, I am trying to help my dad with some truck issues. He lives in another state so I can only help over the phone and inversely can only get feedback over the phone. He has a 100% stock 1988 Chevrolet k2500 light duty. Basically a 1500 with a higher payload. It has a 5.7 tbi and 700r4. The transmission is not that old and is a gm re manufactured unit. The engine is a new gm tbi crate engine. The issue he has is when the engine is put under load say backing up a steep incline or going up a hill on the highway the engine loses power then gains power then loses power then gains power. Its almost like the timing is being retarded. If he gives it a lot of throttle input the engine seems to smooth out and power picks up. His truck is fully loaded with a cap and is filled to the brim with tools so its quite heavy. What are some things that could cause this issue?