Truck Doesnt Run Right

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There is a lot of good, practical advice above. Given the work done on the engine and the onset of trouble, odds are that it is a vac leak (= lean mix) or a timing issue (late fire?) so take the odds and start there. There seem to be literally hundreds of timing/vac/ign component problems for every exhaust restriction issue, so unless you have had the exhaust apart recently or maybe have a really tight rodent nest WAY up in there, get out the timing light. If timing is off, follow the leads noted above. If problem persists once you are certain that the timing is correct and there are no vac leaks, the diagnosis would become much more specific as noted in some of the other comments. Good luck.