Welcome to the site! Always warms my heart to see these older generation trucks still going. Hmm, well, in this instance, still has reasonable potential to still be going.
And you just have to post a question once, we'll find it - promise! :-)
If the engine is dying quick, then I would lean toward an ignition problem. If it kind of sputters and peters out, then would lean toward a fuel problem.
Given what you've described, and without knowing if there are any fault codes (does the 'check engine' light work, and did it come on?) - my first guess would be the ignition module on the side of the distributor. I see that you've already replaced it, but thinking of the potential of getting one that is bad out of the box. AutoZone may be able to check the module with their test kit, but that involves pulling the module again.
After that, the pickup inside the distributor would be suspect.
Suggest to first get your hands on an OBD-I series code reader to see if there are any fault codes that may help narrow things down. These run about $20-$30 if you can still find one. Or a garage or chain parts store may pull them for free or a nominal charge, but it doesn't sound like the truck runs long enough to get it anywhere.
Next suggest to verify the ignition module. Most shop manuals - Chilton's, Haynes, etc. will have the test procedures. This involves the use of a multi-meter - be sure to use a good one. I have little faith in the $10 Wally-world specials. The pickup sensor inside the distributor can also be checked with a multimeter, as well as the primary and secondary sides of the coil.
Also check the distributor shaft, that it doesn't have too much 'wobble' or wear.
If you don't already have a shop manual - I suggest to get one - the thicker the better. This, as well as a code reader and good multimeter, will pay for itself many times over if you do a lot of your own maintenance work.
I tend to advocate testing and checking as opposed to blind replacement of parts. The reasons being:
(1) can spend a lot of money on parts that don't need replacing and don't solve the problem, and
(2) each part replaced that is not part of the problem offers a new opportunity to insert another problem into the mix should the new part be bad out of the box.
1989 F150 XLT standard-cab shortbed 4x4, 5.0L, AOD, 3.55 gears, manual hubs, 31x10.50 tires, 215K miles. Repainted Oct09.
Last edited by wde3477; 12-05-2007 at 04:51 PM.
Reason: more info