My 2003 chevy truck 1500 with a v6 runs good 15miles and after that it starts missing and like something holding it back

Fuel filter stoped up,,,cat stoped up, or the distributor's brain is going out

Im thinking it could be catalytic exhaust problem, oil pressure pegs and truck is sluggish, is the exauhst black and pipe filthy, have the computer read at a parts house to see if anything shows up, i had a 1990 chev, it always ran perfect, no power is the other issue, you can remove the oil cap and if there is lots of blow by or white smoke this is also a good indication of same thing, bad gas can cause this, the pressure is so great on the engine because no exhaust can get out of it,Matt

IF the "check engine" or "service engine soon" light is on. You can take it to most any auto parts store to get the codes read.

Better yet would be to find someone with an actual scanning tool to see what all of the sensors are reading.

IF there is no check engine or service engine soon light on then it could be quite a few different things wrong.

A plugged catalytic converter is a possibility. Another item that i ran across on 3 different vehicles within a day was a bad coolant temperature sensor. All 3 vehicles ran fine when 1st started, but then slowly started to "load up" or run rich. REAL rich.

Turned out on all 3 vehicles there was NO check engine/service engine soon light but after hooking up the scanning tool all 3 showed the coolant temp sensor was reading -40°!!

Yup, the computer was being told the engine was at 40 BELOW zero. The computer took that info and adjusted the fuel/air mixture and timing to help the engine warm up.

While the engine warmed up, the sensor kept saying it was 40 below and made the engine run rich.

This MAY be the problem, but without a scan tool it's hard to say.

Hope this helps.