This is an old post, but just in case anyone else sees this while trying to correct this problem.
If the truck serges while driving a steady speed, it may be transmission related. I have a 99 suburban. Had transmission rebuilt, now at 43 - 48mph the rpms serge about 200rpms every second or so. I'm thinking it could be the torque converter or a vehicle speed sensor.
I have a brand new motor and the truck ran 100%. Transmission came out and went right back in. Nothing under the hood was touched, and now the serging problem.
It's definitely not fuel related. It runs like a scalded dog everywhere else, except in overdrive around 45mph.
If anyone knows anything, I'd love feedback.
Friday, December 18th, 2015 AT 2:58 PM