Trouble at elevation/climbing grades.

Okay, vehicle is a 1995 Suburban. Has a 2 year old GM Goodwrench 350 crate motor (bought new from dealer). Original 4L60E transmission with 325,000+ miles on it now. Drive shaft and rear end are original. U-joints were replaced within the last 5 years. Fuel pump is original.

So when we first got the new engine installed, the truck ran like a dream. I could climb the Tejon Pass in Southern California with ease. However, recently the truck has been having a hard time climbing and accelerating onto the freeway in general. It recently passed smog, a compression check shows the cylinders all look new, and the fuel filter was replaced last month.

Now it's struggling to maintain 55mph going up the Tejon Pass. When accelerating, the transmission drops down to 3rd or 2nd and the engine revs, but that burst of speed we used to get is no longer present. It does accelerate, but it does so very slowly. I'm trying to figure out if it's an engine or transmission issue, or possibly something else. I'm ready to bring it in to the dealer for a diagnostic, problem is we have no grades where I live, so it'll be hard to duplicate that part.

One thing we've noticed ever since we got the new engine, even when it was climbing with ease is that it's a bit shaky. The dealer said there's nothing wrong after 3 diagnostics. The service manager said, it's just exhaust vibration and that any truck from that era (TBI) will do that.

We'll probably do a tune-up and a transmission service within the next few weeks to see if that does anything. But this time around if I take it in to the dealer I'll have them look not into the shaking, but the acceleration.

Any thoughts? Does this sound like an engine, fuel, or transmission issue? Or something else?

Okay, vehicle is a 1995 Suburban. Has a 2 year old GM Goodwrench 350 crate motor (bought new from dealer). Original 4L60E transmission with 325,000+ miles on it now. Drive shaft and rear end are original. U-joints were replaced within the last 5 years. Fuel pump is original.

So when we first got the new engine installed, the truck ran like a dream. I could climb the Tejon Pass in Southern California with ease. However, recently the truck has been having a hard time climbing and accelerating onto the freeway in general. It recently passed smog, a compression check shows the cylinders all look new, and the fuel filter was replaced last month.

Now it's struggling to maintain 55mph going up the Tejon Pass. When accelerating, the transmission drops down to 3rd or 2nd and the engine revs, but that burst of speed we used to get is no longer present. It does accelerate, but it does so very slowly. I'm trying to figure out if it's an engine or transmission issue, or possibly something else. I'm ready to bring it in to the dealer for a diagnostic, problem is we have no grades where I live, so it'll be hard to duplicate that part.

One thing we've noticed ever since we got the new engine, even when it was climbing with ease is that it's a bit shaky. The dealer said there's nothing wrong after 3 diagnostics. The service manager said, it's just exhaust vibration and that any truck from that era (TBI) will do that.

We'll probably do a tune-up and a transmission service within the next few weeks to see if that does anything. But this time around if I take it in to the dealer I'll have them look not into the shaking, but the acceleration.

Any thoughts? Does this sound like an engine, fuel, or transmission issue? Or something else?


the engine sucks in air / fuel and pumps out hot exhaust. if the intake is restricted or the exhaust the engine can not produce power. since the engine is new we will assume the valves/rings . compression is good. to do a quick test simply remove the down stream O2 sensors , leaving the holes open and go for a test run.

could be cat converter or the muffler plugged up. timing must be checked. also intake for leaks though this should throw failure codes. with no codes low power the exhaust restricted or low fuel pressure will do all this.

check what pressure your vehicle requires and measure with a pressure guage.

Sounds like plugged cats to me.

I agree with j cat on the performance. As far as the shaky part did you check all engine and transmission mounts? Ya could have a bad one. Them tranny mounts will give ya the shakes under a load.