Hi guys.  I browsed the forum and didn't see anything on this so forgive me if this issue has been addressed before.  My girlfriends 2000 silverado 4x4 v-6 vortech 5-spd manual,  has a chugging problem.  It comes and go's the dealership cant find a problem... the only fix i have found so far is changing the rotor&cap whenver it starts happening.  It usualy occurs in 4th around 2,000rpm but like i said it could do it on the way to the store then not again for 2-3 days...  Any help would be greatly appreciated.  I have tried a 'tune-up with only temporary results. so please let me know if anyone else has this issue or a solution.

thanks

i have added injector fuel system cleaner to the fuel many times with no results.  the dealership ran a diagnostic and said nothing was wrong at all.  now i know a fair bit about engines and basic fixes but nothing i have tried works just wondering if anyone else here has this problem or knows what it could be .