Temp drops FAST!

I have a 1989 4.0L just rebuilt with ALL new cooling components including the overflow bottle, water pump, 195 degree t-stat, hoses, heater valve, and rad cap. Ever since i replaced everything when i rebuilt my jeep a little over 10,000 miles ago, my jeep will reach about 180-190ish on the gauge, and then drop fast down to 140-150ish at idle. Obviously the tstat is opening, but why does it cool down so fast, isn't it supposed to maintain 195? Going down the road it rarely gets above 150 degrees. Also it takes forever for the jeep to warm up. The heater doesn't blow very hot either. I have put two different tstats in it. still the same problem... Before i rebuilt my jeep it would stay at a constant 195-200 all the time, winter or summer.

Is this normal? i don't experience this type of problem on any of my other vehicles?

Try an OEM dealer T stat. If that does not work, you may be running rich, so check the O2 sensor, or check it first.

If the O2 is working, and the dealer T stat does not help, you have over upgraded the cooling hard ware.