I recently purchased an 89 GMC sierra. It is a 2wd 5 speed. It has 250k on the clock. I bought it for $500 because it has an exhaust leak and an issue with cutting out. I fixed the exhaust leak(manifold bolts walked themselves out). The truck also has new plugs, wires, cap and rotor. When I drove it home, If I lugged the engine even a little, it would buck like crazy until I got the rpms up. I figured that seeing as I didn't know how many hands have been on this thing, I'd start by checking the ignition timing. It was set at somewhere near 14 degrees. I set it to the factory recommended 0 degrees but I had my doubts. It still ran at 0 but it had no power. I then set it to 4 degrees and now it seems to run pretty good. I did have one issue going up a hill at 50mph in 4th gear. I shifted into 5th and it started bucking like crazy. I plan on changing the oil, filling the gas tank, cleaning the throttle body and flushing the coolant before the weekend. Is there something I'm overlooking? Is that bucking normal? I'm a total noob when it comes to tbi.