I can hear the fuel pump kick on for 2-3 seconds when ignition is switched on. Just replaced the ignition coil. Tested the spark with screwdriver and get an orange spark at coil wire and all the plug wires.

Tho only way it will start is to stand on the accelerator then when it kicks over its very rough idling. When I put it in drive it dies. Where should I start with this?

 

I just got done doing a rebuild on the throttle body for my blazer. I didn't find anything obviously wrong, but I was not having trouble as bad as your. It took a throttle body rebuild kit for less then $30, a can of spray cleaner, some random cleaning items ie old toothbrush, and about 3 hours. You could try and test and trouble shoot things like fuel pressure and check injectors, but for the cost and time I just went straight to the rebuild and clean.

 

Got it figured out! It was the temperature sending unit on top of the manifold.