1999 1500 Suburban high speed shimmy and loss of power

[citizenxxx]

I have a strange shimmy and loss of power at speeds of 70 mph+ on 7% and above grades. I don't have any problems at lower speeds on any hills. Only at higher speeds on long steep hills. For example 77 n at the Virginia state line of North Carolina. This is a 7 mile 7% uphill grade of the highway. Halfway up the truck feels like it's gonna fall apart. I slow down into the 50 - 60 mph range and pull into the truck slow lane and it seems to get better. The check engine light pops on (a day later it turns off) and when I get it checked it says a cylinder misfire.

Other than this the Suburban drives like a champ. Transmission shifts great in city and local highway driving (mostly flat with small hills). I was wondering if anyone else had this problem.

The Detailed info follows...

1999 1500 Suburban (4X4)
220,000 miles (been having this problem since around 150,000)
Recently replaced plugs and wires
Recently replaced brakes and rotors
Recently changed transmission fluid and filter (fluid was dirty)
Recently replace shocks all around
Recently had both axles serviced (replaced fluid and replaced some seals)
Had the throttle body cleaned
I'm getting an average of 14.5 mpg city/highway, and on trips I get around 17 mpg average. Not bad for such high milage.

Thanks for any help in advance.

[biggbabysweetz1]

interesting... id be willing to bet its a combonation of things. first make sure your tires are balanced. this is the leading cause of shimmy

[citizenxxx]

It's only in a climb. I can go the same speed on a flat surface or down hill and no shimmy. The tires are balanced. I'm thinking it might be a old tranny. How long does a well maintained transmission last?

[laxman21]

For the shimmy:


What about your drive shaft U joints? Just replaced them and it drives as smooth as silk now. I thought it was the tires.

[citizenxxx]

Thanks. How much did the u joints cost you (parts and labor). I'm going to have that done.

[777stickman]

Can't help on the shimmy. Loss of power, maybe. You listed a lot of stuff you've serviced. The one thing I see missing in there is the fuel filter??

[laxman21]

Originally Posted by citizenxxx

Thanks. How much did the u joints cost you (parts and labor). I'm going to have that done.

$120 or so. had the front and rear one replaced at the same time.


The front one failed inspection and needed replacing, but felt it was wise to do both.



I would have someone look at them before just replacing them. I had the truck back before having them replace and couldn't fihure out what made them bad, but the vibration is gone that came at certain speeds.


I don't know about your truck milage, but mine has 130K.

[biggbabysweetz1]

well i just looked at partsamerica.com and depending one the quality of the u-joint they range from 5 to 30 bucks, if i may i would suggest getting one with a grease zerk. if i were you i would replace ALL of them front drive shaft included, and if you really want to you can have your drive shaft balanced as well to ensure years of trouble free operation (not absolutely required but just a little bit more added insurance) depending on where you go for this it can cost anywhere from 50 bucks all the way up to 200 bucks.