1999 GMC Jimmy Help with cooling problem

Engine Cooling problem
1999 GMC Jimmy 6 cyl Four Wheel Drive Automatic

Hey, I have a 99 jimmy with a 4.3L. I had a problem with my MAF sensor a while ago and until I had scratched the $400 for a new one, I unplugged my old one so that it wouldnt take me 10 minuits to cross an intersection. Drove it like that for about two weeks and got a new one. A few days before replacing it, I was driving accross town(about a 10 minuit drive) and my temperature guage started redlining and then going to zero. (I had a slow coolant leak that I have been constantly topping up) (i pulled off the road, waited 20-30 minuits for it to cool off and went home, got home and smoke was coming out from under my hood. I put a code reader on it which told me that the cts imput was low. So I replaced that and it was fine for a couple km's and started acting up (overheating again) when it is over heating, the oil pressure guage starts dropping (this worries me but am thinking it is because it is getting thinner as it is getting hotter) it seems to miss when shifting, and when it gets warmed up, it wants to stall unless I hold the RPMS up at lights. The tach indicates that it is Idleing around 500rpm when this is happeneing. After it stalls like that it takes quite a few cranks to start it. The plastic piece on the new cts that the harness plugs into ended up melting at some point. I really have not had much luck with this truck and I cannot afford to buy a new vehicle so any help is appretiated,

Thanks