4 speed manual, when i turn off the truck, the engine shakes like it wants to stay on.

any ideas?

autozone told me it might be a vaccuum thing, another person told me the timing needs to be adjusted a little bit.

 

I would check timing first. If you have replaced the cap before it may be slightly off.

 

any idea where the bolt is that holds down the cap so i can turn it?

 

The base of the distributor kinda looks like a tube with a flange on it that goes into the block. Follow the distributor down to the flange at the block. There will be a bolt there that presses a tab down on the flang to hold the distributor in place (I think you need a 1/2in wrench for it).