Changed intake manifold but didn't mark yhe distrubutor. how can i correct this on 1999 tahoe

This motors are hard to get set right even if you marked the distributor for the computer to be able to function right and control the the engine right the distributor needs to be set between -1 and + 1 this leaves no room for error and final placement is usually done with a diagnostic computer

but what you need first is how to get it back in the ball park they will run being off quite a bit but just not very well once you get it up and running u need to take it to someone or somewhere that has a diagnostic computer

Ok now what you need to do is get #1 cylinder on TDC(top dead center ) of the compression stoke put a compression tester into cyl #1 Turn motor over my hand (use socket and ratchet) on crank pulley bolt until you start to read compression on gauge take gauge out and contiune to turn motor over slowly until number piston is at top now put distributor in so when u put the cap back on the rotor is pointing at the number one post on the distributor cap

NOTE: the distributor cap on these motors look at the bottom of the cap you notice where the post for the number 1 cyl is not directly under where u put on the number one plug wire when lining up rotor aim for the post under the cap not where u put the plug wire