Hey all, been lurking for a few months, but I finally bought my first diesel. 99 QC SB auto...it does have 300K on it but I got it at the right price and it runs great.

My first question...It has a newer heavy duty rebuilt trans in it (now about 2000 miles on it) and it seems to dance around on the highway. It'll go a little over 1500 rpm, then back to under 1500, then back over and so on back and forth every second or so...Only does it at higher speeds so I dont know what to think. It has a warranty on the trans, so I'm not too concerned, just wondering what you all think. DTR is a great resource!

Thanks for any help!

 

I wonder if your TC is locking / unlocking - I would have put the warranty to use ASAP, have someone (the builder?) look at it; I assume you're in OD when this is happening? The RPM change would probably be more notable if the tranny is hunting for the TC lockup point- ?

- could be pressure fluctuation in the tranny, PCM communication, electrical noise (I've seen quite a few posts where cleaning up of e-connections has killed transmission gremlins), your OD switch may have an intermittent open in it...

Good luck, keep us posted -

And - Welcome to DTR!