Chevy Cheyenne 2500 vibrating

My Chevy 2500 vibrates when held at constant low rpm's (just after shifting) in an automatic transmission. Either letting off the gas or accelerating seems to clear the problem. It only seems to happen at 45MPH or so. Haven't noticed the problem at all below 4th gear. I can feel the vibration through the entire body, not just the steering column. Any help?

Edit: Forgot one thing.. these symptoms didn't appear until a day after I had to drive through some rather large puddles (more like flash flooding). Probably about 4-5 inches in depth. Thought that may help to resolve what the problem is.

Can't seem to get the post right. '92 Chevy to be exact if it makes any difference (don't think it does)

Our suburban had that problem. Turns out a u-joint was twisted all to hell. I don't know if thats your problem but its worth a shot

That doesn't appear to be the problem. Looked at both U-joints and aside from being dirty, look free of any twisting or cracking. I'm thinking it may have something to do with the CV Joint. Sound like it to you guys?

First off, welcome to the forums. Well, I hate to sound negative but it might be a lot of things. Off the top of my head, Are sure the engine isn't missing because of the water. You usually wouldn't know at high R's. Do you have a two piece driveshaft, maybe the carrier bearing went, that isn't noticable at low speeds or high speeds, only right around 45 mph or so. The u-joints could go bad without them being cracked so put your truck in neutral and move your driveshaft to see how much play is there. When my CV's went out, I didn't notice a vibration but there was a hell of a clicking coming from the front end when it was in 4 wheel, so you might want to see if it does that. Also, (not likely but possible) could water have gotten into your rear end and screwed your gears? I'd check your rear end out. I can't think of anything else right now, hope I at least pointed you in the right direction.

Thanks Pewter, this at gives me something to move on. I pretty much sat around scratching my head for a while looking at all the usual suspects. I must admit I'm mechanically-impaired for the most part. I'll take a look at what you mentioned. Now that I have something to move on I'll be all over it <grin>.

Oh, and thanks for the welcome to the forum. I've learned quite a bit just reading through here. Thes forums have been a big help on some past projects.

Have you ever thought about the TCC being bad or having a faulty connection after the water incedent? This is the Torque Converter Clutch. I locks your Torque Converter in high gear so there is no slippage in your trans going down the road. there is a plug on the drivers side of your trans with four wires coming out of it i believe (It may not have 4 wires, but it is a 4 wire square connector) unplug it and drive it to see if the problem still exists. This WILL NOT HARM YOUR TRANS, if only done temporarily! this is a TEMPORARY FIX, don't leave it unplugged if this fixes it, you will eventually tear the trans up. If the shake stops your TCC is at fault, if not it's good and plug it back in........and look elsewhere.

I didn't even consider that aspect. I'll give it a try and see what happens. Haven't been able to test the past speculations yet, time constraints and all. I forget that even "old" vehicles may still have electrical components that could cause problems, I'll definitely look into it. Thanks!