My '88 B2200 started running hot once it got like 175K and 20 years old. It did not lose coolant, had trouble on long freeway uphills in Arizona summer with AC on. I tried thermostat swap, chemical flush of radiator, made absolutely sure that all the air was bled out of the system (jacked up front, ran with cap off, topping off, for 20 minutes), no effect.
Then I fixed it. How? I purchased a brand-new 2-row radiator for it, replaced the old 1-row radiator, solved the issue immediately. I have the all-aluminum 2-row radiator from O'Reillys, 2-row was originally used on the automatic trucks, but will bolt right into the B2200 frame. Since mine was 5-speed, I did have to drill four holes in the radiator bracket. "New" fan shroud overlaid on the Murray 2-row radiator. Red arrows show Murray shroud mounting holes. Blue arrows show where I drilled my own 1/4 inch holes, so I can use 6.0mm x 1.0mm bolts/nuts.