needle jumping and warning lights

I recently purchased a 1998 Pontiac Transport van with approximately 140,000 miles on it. The original engine (V6) was blown, but was just replaced by another engine (V6) that only has 50,000 miles on it. The alternator was also replaced. While returning home with the van (6 hours away), I noticed all of the needles on the instrument panel began to jump. After doing this for a while, they would stop and everything would seem to be fine. Toward the end of the trip, the Traction Control System Warning Light, the Anti-Lock Brake System Light, and the Check Engine Light came on - sometimes together - sometimes separately. The temperature would also get a little hot, but would fall back to normal after the "jumping" would stop. The vehicle also began lurching at one point, but that stop after a minute or two. I would appreciate any help or advice you can offer. Thank you for your time. Allen