My buddies 2003 Tahoe, with the 5.3L Vortex motor, was acting awfully funny yesterday and I'm hoping maybe someone has seen this problem before....

We were on the highway (in the mountains of CO....elevation was about 8,500 to 10,500 feet) yesterday and the motor started to loose power. It was kind of funny though. We were on an almost flat section of road....not pushing the motor at all....and all of the sudden it felt like the motor was struggling to keep up...then it lost all power. We got the truck pulled over and it was idling barely, I got out and it sounded like a cylinder (or 2) weren't firing. Then the motor quit. My buddy tried to restart....it took 2 or 3 tries, but it did restart and the engine sounded fine but, it didn't have full power. Without many options, we continued driving with this low power problem.

Over the next 2 hours, the motor quit 3 more times. All the while the motor is feeling pretty weak..... We could barely get up a few of the bigger hills. After we get out of the mountains (elevation is now about 6,000 feet) the power seems to come back and the problem is gone.

The engine has 70,000 miles on it and is very well maintained by the dealer; and the check engine light is NOT on. (unfortunetly for my buddy, he's on a road trip visting me and is 1,800 miles away from home or the dealer)

Does anyone have any idea's??

Back in the late 70's...... I saw a really similar problem with a Buick my Dad owned. It ended up being a plugged fuel filter. I'm going to replace my buddies fuel filter on this Tahoe, just for good measure. But, I'm hoping someone else has had a similar problems. Anyone?

Does it have a throttle cable or is it drive by wire if it is drive by wire a very common problem is the yellow wire on the TAC breaks in side the insulation 4-5 inches from the TAC check all the wires at the TAC the yellow wire is the most common but I had one monday break the green wire

03 should be drive by wire. But if it's not throwing a code I would think the fuel filter is clogged or fuel pump. But you could hook a scan tool up to it anyway and check for codes.

If the check engine light was on and flashing then it would be in limp home mode and have reduced power.

I did a scan of the ECU and it came up empty. I wasn't expecting anything though, the "check engine" light was never on.

I did replaced the fuel filter. Mostly cause it was cheap and too obvious not too. ....when I got the fuel lines off a lot of very black gasoline dripped out......My buddy is on a cross country road trip and has been kinda slutty about where he fills up. So......at this point I'm pretty sure it's the fuel filter.

What is the a TAC? What does it do, and where is it?

Throttle Accuated Controler it opens and close the throttle blade on a drive by wire setup

Throttle Accuated Controler it opens and close the throttle blade on a drive by wire setup if you don't have any code or a reduce power message in the Drivers Information Center than this is probably not the problem

I am going to have to second the nomination for a fuel pump or fuel filter. For some reason the older Tahoes were known for this, but haven't heard it much about the new body style.

Best way to check the pump is take it somewhere that can check your fuel pressure.