GM-GMC: wont start, 1990 chevy 1500, auto parts stores

Question
--------------------------------------------------Funny.......... when I got home last night the truck started up. I knew it didn't fix itself so I looked into it a little. First I took the cap off to check the rotor. The pin that pushes down on the rotor was broke off and sitting on top of the inside of the rotor. I replaced the cap and used a new rotor, and thought the problem was fixed. When I came to work this morning the hesitation was still there. Could it be a sensor? I have not changed a thing on the truck since I've owned it, electrical wise that is.
Followup To
Question -
I have a 1990 Chevy 1500 that started giving me fits last night comming home from work. It was a hard start also. I cranked on it for a while, I even gave it some gas by giving it some throttle, but it finally started. On the way home I could not give it a lot of gas as it would hesitate. If I gave it just a little it would go. I could down shift and it acted fine in the upper rpm range. Well, it didn't start for me this morning. I put a new fuel filter on it last night but is still did not start. It didn't even hicup when I squirted starting fluid in the throttle body.
Answer -
Your problem is more likely to be ignition-related, especially since you stated that the engine would not fire using starting fluid.

It may be the ignition module or, if your vehicle has a distributor, the cap and/or rotor may be bad.  The parts are available at most auto parts stores.  

Answer
Yes, a sensor can cause the problem you are describing.  One of the most failure prone is the oxygen sensor.  Without the vehicle will run, but often runs poorly and consumes more fuel than normal.

The oxygen sensor can be hard to remove, due to its location in the exhaust system and the fact that it often rusts in place.  There should be a diagnostic code indicating a problem with it, but if you do not know if it has ever been changed, changing it might help the performance of your engine.

The other parts of your emission system on your vehicle may also be causing problems.  It might be best to take the vehicle in and pay for a full diagnostic check-up.