Hi all,
Im new here and have a issue with a 90 model 350 suburban with about 160k and 373 rear. I got it from the original owner a few months ago . It is in fantastic condition all around it runs beautifully BUT it doesn't have nearly the power of any other 350tbi Ive owned. I'm at a loss because it has less power then my two current 350 tbi vans one of which has 342 gears and the other has 308's and both have well over 200k.
I don't really notice it with out a pulling a trailer. I have a small business and almost always have a 5x8 or 6x12 enclosed trailer wherever i go. Last week I needed my rarely used 7x16 enclosed and pulled it along a route im used to driving with a van. The route involves a two mile uphill grade that my vans will shift into third and allow me to maintain speed, the suburban refused and actually went into second a few times struggling the entire drive. I left the trailer on the job and picked it up later with a van. I dropped the suburban with the local mechanic to no avail he said there's not a thing wrong with it.
Im not a mechanic but have learned my way around these motors enough to do tune-ups and such. since ive got it i've done or had done the following....plugs wires cap, fuel pump and filter, air filter and complete rear end rebuild. I've put close to 10k on it and like i said before it runs great but i don t know where to go with this power issue. The posts ive read about power loss usually involve horrible mpg's but its doing fine in that aspect 13 city 18 hwy empty and 12 with a small trailer around town which is on par with my vans.
Any Ideas?? thanks

 

My guess is either tranny or fuel. A 3.73-1 ratio isn't bad for highway or even towing. It isn't however a 3.42-1 for towing. Tune up might also be in order.

 

Im confused. Are you suggesting a 342 is a stronger gear for towing?

A light tune up was done within the last couple of months. It runs really nice just the power issue

 

3.42 is a lower ratio, thus more torque to the drive train/trailer. Tuneup, was a suggestion as you didn't state such.

 

Im not a mechanic, but the math would state the opposite. Am I wrong?

 

The pinion turns the same, the torque/output ratio is less with a 3.42/1 than a 3.73/1.

 

Which is opposite of what you said in your post #4. IOW the 3.73 would be better for towing but probably not as good for mpg.