99 Envoy Front Diff and Tranny Problems

I have a 99 Envoy with 68k I bought used a few years ago. Since then, nearly all of the drivetrain seals have leaked on it. The leaks seem to coincide with long road trips... not sure if there's a correlation or not.

The rear diff leaked at all three seals and required a re-build (under exteneded warranty) at 49k. I took it to a dealership and they also replaced both front hub bearings (I thought my tires were loud!). I was so pleased. It rode so quiet and smooth.

After a recent long road trip on it, I noticed a bearing noise again while driving. I checked and found all 3 front diff seals were leaking as well as the seal coming out of the transfer case. I took it back to that same dealership who rebuilt the front diff (replaced all bearings and seals in it), replaced the transfer case seal, and replaced the inner left cv-joint (they found a leaking boot). It still was noisy. They then replaced the right front axle assembly and right shaft tube. Still noisy. They then replaced the hub bearings (again) and that fixed the noise. They did a lot of the work for free since they couldn't get it right the first time. Still pricey though.

It's still not right though. There seems to be a vibration now that gets worse the faster I go. I haven't taken it back yet because I've lost faith in that dealership, but I might since they'll probably not charge me much if anything. I just bought a Haynes manual and have ordered a Chilton's also. I'm ready to fix it myself. Anyone have any idea what that vibration could be? It feels like a bad u-joint would feel, but the u-joints seem tight. It could be that they didn't match-mark the front drive shaft when they replaced the transfercase seal. What do you think? If that's it, are there any tricks I can try to fix this.

Next... I am going to replace the leaky rear transmission housing seal. Anyone know of any thing I should watch out for or any lessons-learned to share?

Finally, I have noticed that my transmission has started acting up since a 60k flush/fill at a dealership. It seems to clunk into reverse from park, it has slipped between 1st and 2nd on a few occasions, and it seems to clunk into 3rd. If I accelerate harder, it rev's higher/longer in 2nd and doesn't clunk into 3rd as hard. Also, when I'm slowing down to a traffic light at about 25mph, and it turns green and I hit the gas, it clunks some of the time. Anyone have any thoughts on that?

Thanks

It sounds like the noise/vibration could in fact be your universals. I had a similar problem with mine and when I checked the u joints, they were tight-too tight. I replaced them and no problems since. As far as your wheel hubs go, that seems excessive to me. I just changed mine at 180,000. I only did that because I had the front end appart for ball joints. Just a tip, if you try to replace your u-joints, they don't just press out like some of them. You have to press one side out at a time. Can be quite challanging if you never have done them before.