92 s10 temp fluctuating

[NtheFamily]

Okay, I have a '92 s10 that I bought last year with 139,000 miles on the 4.3. I have installed a new radiator, new upper and lower rad. hoses, new water pump, new thermostat and new oil pressure sending unit.

Few questions:
1) When I drive it somewhere, the temperature gauge will climb to about 210 or a little higher then go down to about 195 - 200 during the first several minutes or approximately first 20 miles of driving it (been doing this since I bought it even before I put the new stuff on). I put a 195 thermostat in it. Why does the temperature fluctuate so much? Will this harm the engine since the temperature does go down?

2) I replaced the oil pressure sending unit since the original one was leaking. When it is firsted cranked up and I drive it for 20 miles or so, all is fine (50 - 60 lbs on oil pressure gauge), but when I stop at a red light it drops to about 16 lbs. Is this normal lbs. of oil pressure at a stop? If not, what is normal?

3) Can you by new 4.3 motors for it from Chevrolet that is an easy swap and if so, has anyone priced them ?

Other than that the truck runs great, gets great gas mileage (from what I'm used to getting from my '85 4x4...which is 9 mph) and is not banged up.

Thanks for all and any ifomation.