1995 Ford Aerostar overheating with new water pump & go

Hi,
On my temp. Guage (NORMAL) It never used to go over the O or R on temperature.
My water pump started leaking so while I waited for a pay check I used 3 containers of a gold (glittery) looking (stop leak) over a one week period.
We finally changed the pump and it still went to extremely hot after driving for 30 minutes.
I had the thermostat checked & the mechanic said it was ok and sent me to a radiator specialist who told me to go home and flush the radiator.
I removed the lower hose and flushed it 3 times.
It still over heats although it got a little better.
The only other symptoms the Aerostar is having is an occasional puff of white smoke at start ( maybe 3 out of 10 starts) and thats only at the start of the day, after the first start it gets no smoke while engine is warm. And now I occasionally hear a putting sound at the engine (only sometimes) while in drive.
Please help I can only drive 30 minutes at a time.
Paul 305-609-3945 or 305-891-1820
Thanks, My mechanic can'tfigure it out.