VIBRATION AT 60MPH OR BETTER

I would suggest that you check the wheel bearings for condition and adjustment
have the cv joints checked for that drive axle
check all suspension ball joints and steering ball joints on that side

If it blinks and goes away, it is a "random misfire" that culminates before the light begins blinking. Sustained misfiring will result in a code, and the light staying on. If the light blinks and goes away, the issue is intermittent. Your problem usually occurs under acceleration or heavy load. The issue can often be solved with new spark plugs, though it could also be dirty injectors. The injectors on that vehicle are infamous, however I have been able to fix your problem with repeated use of highly concentrated fuel system cleaner. I use at least 3 times the recommended concentration of whatever cleaner. People rave about Sea Foam. I have used it and it works -- though I can't say whether it worked better than other brands I have used. I have owned 3 Blazers and 2 S-10's, including my current 2001 Blazer LT.

sounds like a worn out transmission mount try rocking the ****** up and down and if the play in the rubber mount appears excessive this can cause all of the stated problems

Try to rev the engine while at neutral if you get the same vibration to pinpoint if its from the engine or the drive shafts. If the issue occurs at a certain rev it may likely be the variable valve unit. Check if possible if you can get errors from the computer.

The A/C compressor cycles on and off as you drive, sometimes 4 times/minute. This is normal.
If it is worse than it used to be, maybe the compressor is the issue. How does it feel if you turn off O/D so it does not shift into 4th gear, but stays in 3rd gear.

either need throttle cable adjusted or fluid and filter changed ASAP before any more damage occurs

The OD is a extra gear do you need it not really you can drive 150 miles if anything its the switch button that went out

You have warped the rotors. Hard braking and a heavy foot on the brake pedal at stops will do that. See a dealer for the other.

I would start with plug wires rubbing on something and created a short.and is not compleatly worn through. a cheep place to start. good luck with it.

Change plug wires. Most often, plug wires will only short out when they are under load, so you don't notice anything until your motor is doing a little extra work.