PROBLEM SOLVED
After pulling the rest my hair out.I decided to change the motor mounts for the fun of it.Turns out the passenger side was grounded to the frame.There was some improvement but vib was still there. I just got through changing out the transmission mount.It had collapsed on it self, that wasn't visible,but comparing it to a new one,big differance.Hind sight is always 20/20.
Runs GREAT!
Hope this is useful




89 s-10 Blazer 4.3 167000 miles automatic TBI
It idles good with a slight vibration, gets pretty bad at 1500 and 3000.If you hold rpm's steady at 1500 the vibration drones.If you are driving under light acceleration the vibration isn't to bad but if you do a half throttle start it really shakes and if you floor it ,it feels like it's gona blow up.Driving along at 55 and shift to netrual and coast it's nice and smooth. Years ago someone put eggs and beer down the gas tank.Runs bad on beer, I pulled the tank cleaned it out and changed the filter. Drove it a bunch, still ran rough' ran fuel sys. cleaner , no help.

This is what I've done Lately.
Replaced fuel pump in tank
Replaced fuel filter
new fuel pump relay
new oil pressure/fuel switch
Fuel pressure 13 PSI
rebuilt fuel regulator
New gaskets and o rings
New plugs , wires, cap,rotor, pick-up, internal coil
set timing
replaced harmonic balancer
I have removed the belt to eliminate fan, alt, etc.
unbolted the torque converter
rotated torque converter to other 2 positions
motor and trans mounts good
compression ranges from 145 to 155
Vaccum holds pretty steady 16-17 in. at Idle and steady at 18 at 1500 rpm
Can't find any vaccum leaks
changed filter screens on injectors
I can see dribbles ( drops kind of connected) in the Injector spray pattern and the fuel runs down the sides of the throttle bores from the spray pattern.I can't see a well defined cone pattern.

Any idea's would be much appreciated