Ben,

The exhaust could have been clogged, causing some of the issues. I would check that... a 2.5" exhaust really helps these cars a lot. I would also check the harness around the coil... see if there is any damage, dry rot, ect. (this could go for the entire harness as well). The tach filter can cause a world of problems. Lastly, what chip are you using? Was it a custom chip or stock?

Were the numbers at the rear wheels? If so, that's not bad. I would guess GM figured the stock numbers at the flywheel.

hoop