Sausage Fingerz

I have an overheating issue on my 1984/ 110. It has a 2.25L petrol engine. The truck has aftermarket Revtec dual cooling fans for the radiator. I noticed they were not working recently. I first replaced the t-stat, new coolant, and then the fan relay. The temp gauge has been a bit erratic, pinning the needle in the hot area, then dropping to normal randomly, then moving to hot again. To get the fan running, I took the dust cap off the sensor, turned the adjustment screw 1/4 turn and the fan kicked-on! I am still getting a hot gauge though, with the engine wanting to stall when I come to a stop. Is this the sensor or maybe a water pump? Is there possibly an air bubble and how would I bleed?