1993 K-1500 Vibration

[Rohon]

Hello to all, have a 93 K-1500 with 350 engine, auto trans. My problem is when your at cruising speeds a vibration will start, and if you let off the gas it goes away, if you step on the gas as to pass, it will go away also, this happens at different speeds. Replaced the u-joints so far still have this going on, and it seems to me it is coming from the back of the truck, my son says it is coming from right behind the cab, anyone with ideas as to where to start looking for and at, for this.

[1993Suburban]

Is there any certain speed it likes to do this at? My '93 Burb would do the same type of thing around 38-43 MPH. It would only do it when while cruising steadily at that speed. I took it into the transmission shop and they told me it was most likely one of two things, or both. The 4L60E tranny has a Torque Converter Clutch lockup solenoid / switch. When it gets wear it will switch on and off, thus locking and unlocking the Torque Converter, creating the little vibration you are feeling. My '96 does this also, however it is not very noticable (only to someone like me), and it has a rebuilt transmission. They tranny shop said it was due to the engine running just a little rough (159,000 miles). When the Torque Converter locks up, (it does this around 40 MPH), it brings the RPM's way down, and since it is locked up, vibrations from a rough running engine can be felt in the drive line. This might not be the problem, but it sounds similar to mine. Could also be something like an out of balance driveshaft or tires. Just my 2 cents.