slant 6 gettin WARM

Welcome aboard!
I'd start by putting the correct t-stat back in. The stock temp is 195*. The lower temp t-stat might be making the overheating worse, for example, if the water doesn't stay in the radiator long enough for it to cool down, when it gets back up to the thermostat the water won't be cool enough to shut it...t-stat stays open and the even hotter water flows through the radiator and doesn't get cool enough the subsequent times either...temp just climbs and climbs.
Temp issues while sitting/driving slowly are typically caused by air flow problems.
What size fans are on there? and how are they set to turn on?