You have to remove the air conditioner and bracket to get to the thermostat. Its a bit o work.
While in there you might as well replace the thermostat, & the bypass hose (Vaseline is your friend), and maybe the top rad cooling hose. You will want to once you see how much taking apart you have to do to get at them.
The two sensors in there cost less than $20 each. There is also an intake air temp sensor on the passenger side of the intake just above the thermostat which I changed. I forget what it cost but it was pretty cheap.

 

I forgot to mention that yo do not have to drain the AC. You can remove the brackets and lay it over to the side the hoses are long and flexible enough.

 

My 91 2wd 8 ft bed 3.9 3.55 gear set automatic with A/C driving from oregon to the Mississippi golf coast got 27 mpgs at a steedy 65 mph got 19going through the mountain passes in Arizona and neveda and new Mexico. Its almost worn out now it just clicked 93, 000 miles on the odometer

 

Hmm ..

Wonder what mine is at 283,000+ miles on ITS odometer ...

RwP

 

Well seasoned lol

 

1989 untouched, on highway@20 mpg

 

Get 20 with my old 89 4x4.

 

Bought truck new in 5-'95. 14 mpg from then up until now, hi way or city. Can't improve it. Why?

 

Got a new truck, guess i should post my new mileage? lol

I get 9mpg around town with a 5.9l Magnum. Ram 2500 axles, so it has about 12" of lift, and it's on some aggressive 33" mud tires. The axle tags say it has 4.55 gears, but i'm not positive. Have yet to jack up the rear end or pull of the cover and check

 

95 2.5L 5spd ave 25-28 with most driving @ 40-60mph