After hundreds of bucks in repairs and hundreds more in parts, yet more problems on 1991 GMC Sonoma

Sorry if this is a data overload, but I want to be thorough. As you can see in my previous questions, I've had a lot of problems with my pickup. Most of which I thought I've taken care of. I've had two mechanics work on my truck. The first turned out to be a shade tree mechanic, that I found out had no shop, and did all the work he did on his duplex's driveway. He replaced the flexplate and transmission mount, and he disconnected my steering column to install the driver side exhaust manifold because he broke the bolts on the flange and had no torch. He had me pay extra on labor for that. On top of this, he replaced my rear transmission mount, and left my interior trashed (along with my headlights shorted out). Since then, I've gotten the headlights to go. Had to replace my positive wire from the starter to my battery because this guy left it next to my exhaust manifold (so it shorted out in the middle of an intersection). When I start the truck, you can hear a low metallic flutter, then it stops as the truck idles and drives. I checked underneath and the flexplate seems to have a slight "wobble". I was told that torquing the flexplate it tricky and should be done by a professional. So far, no problems have arisen yet. Next, took it to another mechanic to have a used transfer case put in, because my old went to crap. It would grind and grind. The newly installed transfer case is in the 2WD position, but it seems like once I go over 50 mph, the truck would shimmy. I thought it might be the tires, so I took it easy. Next, I had the same mechanic (who replaced) the T case, replace both of my front motor mounts. I was always apprehensive about driving on the highway, so I took it out for a spin onto the highway. As soon as I got up to speed, here's what happens next. Front end up vibration gets greater and greater, GPS reads 65 (my speedometer is saying 80, but the cable has been off since I've owned the truck). I figure if the tires were out balance, I'd be having a hard time steering. It wasn't hard at all. Then as the vibration got to a certain point, I hear on the passenger side.... PING! A clatter noise, something metallic bumping under my truck. I pull over to the shoulder, and was able to walk back to the point of when I heard that noise. I saw nothing. I went of the nearest exit and pulled into a gas station to check under the hood and I didn't see anything wrong. Crawled under and I noticed that a few drops of tranny fluid were dripping on the pavement right away, then stopped after about 4 drips. I checked the bell housing and starter bolts I replaced, that once had fallen out. They were all there. Checked the tie rods, shocks, and ball joints. All seem fine. Then I noticed something odd. My new CV axle on the passenger side had a problem. The upper boot was completely torn off. I bought it brand new in December and had it installed by Commercial Tire. CT said it was a manufacturer issue and nothing I did or all the mechanics who had worked on it before. In other words, just bad luck. I am curious though. Would that torn boot cause a bad vibration at highway speeds? I forgot to ask the CT mechanic that. Is it also possible that the used T case I had put in, is stuck in 4Hi or Lo? It seems to shift normal, while in neutral. Ever since the first mechanic worked on my truck, the 4Lo LED is constantly on, and it didn't used to be. Hence my curiosity. Thanks in advance as always.

by in Nampa, ID on March 15, 2012
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1 answer 1 comment
ANSWER by , March 16, 2012
COMMENT by , March 16, 2012
The first mechanic, yes, but the situation was really odd. It would take too long to explain that horror story. The second mechanic simply misunderstood me from before (about the light) and is willing to take a look at it Monday for free. He did replace the transfer case and may end up fixing the problem for nothing or next to nothing. As for the CV axle, that will be taken care of Saturday afternoon. And yah, that was a mouthful. :) I like to be as detailed as possible, since diagnosis in text is so limited compared to real world observation. I am surprised they don't have a photo album here, so guys can upload photos from their cellphones, to show an easy to see (external) problems.