Suggestions for fixes please?

I'm pretty sure the over cooling is leading to the first problem. When running around twon etc, the gauge never gets above the top of the white block at the bottom of the gauge. If on a long run (ie motorway), it will drop to the bottom of the white block.

Viscous fan spins freely, not seized. There is a thermostat in there (put a new one in just in case while housing was off).

Replaced the VSS, but no change there.

Car is also a bit lumpy pulling away hard, or going up hill.

What else is there to check / look for. Car was serviced fully not long after I bought it a few months ago.