Does it have a code showing? When mine did that, I did the JBfP electric tune-up. Basically, disassembly of the connectors and hitting each wire/connector with a soldering iron, make sure the wire itself wasn't loose in the terminal. Tedious, but it solved all kinds of weird maladies that mine had when I first got it.

89 SWB, V-6 5SPD, OME Shocks, 16.5X37's, 2"BL, SR axle, Gen2 brakes, Lincoln w/Superwinch