possible fuel injector problem but not sure

Since I purchased my 1992 Bronco about one year ago, it has been having a strange intermittent problem. Its pretty hard to describe but I'll do my best. sometimes when i first start my truck in the morning, it will run rough, like its running on 7 cylinders rather then 8. if i drive it like that and come to a stop, the RPM will start going up and down like its about to die. if i go and park and let it sit for about 10 minutes or so, and restart it, it will run fine. it also does the same thing when the truck is well warmed up. for instance if drive it for a good half hour, then stop at the store and turn it off, 15 minutes later i start it, and it does the same thing. I have aked some mechanics what they think, and they say it could be a bad fuel injector and they want to diagnose it. but i want to be sure before i drop another $700 or so to get it fixed. i have also tried many fuel system cleaners including lucas oil fuel sytem cleaner, STP, etc. I also have a Jacobs electronic ignition installed. the previous owner installed it himself, could that be a reason? or is it something else?

This problem has been very frustrating, and if anyone has a solution or some helpful insight, it would be VERY much appreciated.
THANK YOU.

THE BEST ADVICE I CAN GIVE IS TO TAKE IT AND HAVE THE COMPUTER SCANNED FOR CODES..COMPARE PRICES AND IF THE DEALER ISN'T THAT MUCH HIGHER THEY ARE YOUR BEST BET FOR A DEPENDABLE SCAN ALSO YOU CAN ASK THEM TO PRINT OUT THEIR FINDINGS FOR YOU..
THIS WILL SAVE A WHOLE LOT OF TIME AND MONEY FROM PARTS SWAPPING AND GUESSING.
SOME TESTS YOU MAY WANT TO DO::
TEST YOUR FUEL PRESSURE
CHECK YOUR ALTERNATOR OUTPUT(THIS IS VERY IMPORTANT FOR COMPUTER CONTROLED IGNITIONS-YOUR LOCAL PARTS STORE WILL NORMALLY DO VARIOUS TESTS FOR FREE SO LOOK INTO THAT..)
CHECK TO MAKE SURE YOUR JACOBS IS PROPERLY GROUNDED AND ALL THE WIRING IS GOOD..
HAVE YOU CHANGED YOUR FUEL FILTER?
CHECK VACUUM LINES
CHECK FOR PROPER EGR FUNCTION
SEE WHAT I MEAN :eek7: HAVING THE COMPUTER SCANNED FIRST CAN REALLY SAVE TIME...IT IS WORTH THE MONEY AND CAN ALSO DIAGNOSE UNRELATED PROBS. AS WELL..