97 Sierra Poor Performance

[97GMCSLE]

I have a 97 GMC Sierra XC 5.7L. It is all original and have noticed it just doesn't have the get-up-and-go that my wife's 99 suburban has. Both around 85,000 miles, both with the 5.7L. I did tune up, plugs, wires, cap, rotor, checked codes. I have been told the catalytic converters (5.7 has two) can clog up and resulting in sluggish performance. Anyone replaced theirs resulting in better performance? I'm in California, so I can't take them off.

Any help, comments appreciated!

[horse482]

You cannot take them off, but you can put performance cats on there. Yes they will plug and when they do it will run very bad.

[97sle]

Did if use to have good get and go and then 1 day it didn't or what? Because I have a 97 SLE with 5.7L short bed, standard cab with 108,000 miles and it runs like a champ and gets up and goes with no problem. But for some reason other trucks that me and my friends have driving that have the same set up don't seem to have the same power as mine, IDK why.

[97GMCSLE]

It seems to be slowly losing the pep. It does fine on the flat freeway, but going up up mountain roads/highways at 50-55 mph, it seems like it just runs out of power. it down shifts to 3rd and won't pick up speed and the valves/lifters start pinging. So I am trying to figure out if it is tranny shifting problem where the shift points need to be higher/lower, or if it is a restrictive exhaust or something motor related. I pull a 21' camp trailer and it makes the 5.7 feel like a 4cyl on the hills or picking up speed. I am going to perform an exhaust pressure test before and after the cats to determine that.
thanks for the replies!

[2000CAYukon]

Originally Posted by 97GMCSLE

It seems to be slowly losing the pep. It does fine on the flat freeway, but going up up mountain roads/highways at 50-55 mph, it seems like it just runs out of power. it down shifts to 3rd and won't pick up speed and the valves/lifters start pinging. So I am trying to figure out if it is tranny shifting problem where the shift points need to be higher/lower, or if it is a restrictive exhaust or something motor related. I pull a 21' camp trailer and it makes the 5.7 feel like a 4cyl on the hills or picking up speed. I am going to perform an exhaust pressure test before and after the cats to determine that.
thanks for the replies!

If the cats were clogged, I think you would also see performance issues on the freeway. You can test the back pressure with an exhaust back pressure gauge.

Have you had the cam retard set with a scan tool? The timing is not adjustable and the cam retard is needed for the PCM to change the timing.

The dist gear can also be worn causing it to run rough. Has the fuel pressure been tested? The fuel pressure regulator is a common problem and can leak fuel into the intake causing drivablity and warm startup issues. If the fuel pressure is too low, it can lack performance.

//2000CAYukon

[97GMCSLE]

I had the cam retard checked right after I did the intake manifold gasket. It checked out good. I didn't consider the fuel pressure regulator. I'll look into that as well.

Thanks for the help.

[2004vho]

How about installing a new fuel filter, PCV valve, and a can of Sea Foam into a 1/2 tank of mid-grade gasoline. Then another can of SeaFoam into the PCV hose/Throttle body. Try it out and get back 2 us here....