Okay friends - I think problem is solved finally. So yes you saw that I took it to CBA for the engine mount replacement, that didnt help at all. This was before I decided to work on the car myself.

So earlier the first thermostat was changed to 180F probably at around 75k miles (from the GM recommended 195), then I did another flush and another and and so on finally due to the overheating issue due to the bad radiator, decided to change the thermostat as well , this time I changed it to 195.

Now there are very jerks , in fact the jerky movement is slowly ceasing.

Also I am using the high mileage Lucas Fuel Treatment additive along with premium 93 gas, which I will use for probably 1000 or so miles.

A few things, the noise has come down considerably, the engine does run hotter, 2 bars below midway (with the 180F it used to stay pegged at 1/4 ), but pickup and smoothness has returned, I now hear the same engine that I heard when I bought it 10 years ago!

<Touch wood for all the positives in the post !>

Thank you!