93 Es300 Rough Gear Shift When Cold, loss of power, acceleration

Hello gurus,
I have a 93 es300. When I start the car in the morning or after 5-6 hours of rest, the car gives a jerk when shifting from first to the second(could be 2nd to 3rd too...). The problem is less felt if I let the car get heated up for about 5 minutes and start driving. It gets better as the car gets heated up. I feel very slight jerks for shifting of other gears too.

My car has 120K miles on it and has new timing belt. I have recently done transmission service on it, but no use. I have also taken it for a trasmission check and they reported no problem in transmission. I have observed considerable loss of power and acceleration from when I got the car around 60K miles. One more observation is that the problem got aggravated after changing the timing belt.

I can't seem to find the source of the problem and am worried that I might be damaging something internally by continuing driving without fixing

Please help....

check if the timing is correct, car will run really bad if the timing is not correct.

Thanks for you reply. I'll try that. But does this explain loss of acceleration.

If the the timing is not correct you will feel a lot loss of acceleration for sure.