I have a 1989 straight 6 with only 72,000 miles. When I start the truck up and sitting at idle, also when sitting a stop light the truck has a small shake and will shake the whole truck. This afternoon it actually shook an then the truck cut off. Any help?

 

you've got a number of cylinders that arent firing properly for one reason or another. pull your plugs and check them out, do you have any smoke coming out of the exhaust, if so what color?

 

I see no smoke at all

 

Check the plugs wires cap and rotor. Check all the wiring to the injectors (I think that's injected?) for broken or chewed wires. Check all the vacuum lines.
After that you'd want to do a compression check - or maybe you want to that first. It's pretty simple on a 6 cyl. And you can throw new plugs at it while you're at it.
If you eliminate a compression problem right off, then it's just a matter of investigating/testing things till you find the problem.

 

I took it to the shop today, they will start on it tomorrow. Gonna start with oil change and go from there.

 

Now is a good time for you to buy a Haynes repair manual, and or search youtube on how to do these things yourself. These old trucks are easy to work on but can become a 'money pit' if you pay someone else to do the repairs

 

Turned out being the fuel pump