Crappy running engine - What to do next?

[kcackler]

We've got an 86 3/4 ton GMC sierra truck. Since we've hooked up the proper vacuum lines and the choke, the truck is running better, but still not great. We've got a really really rough idle, and that is the main problem.

So, if you had just bought a truck and it was running like crap, what troubleshooting steps would you take, in order? I don't want to go spend money on a tune-up right off the bat if there are other steps that should come first in the troubleshooting process.

Thanks,
Kevin