E4OD-O/D light flashing

'96 heavy 250 with low miles on complete trans. O/H. O/D light is flashing and shift quality is poor (read rough & abrupt ).Truck is used for plowing and firewood hauling,but always worked in low range/low gear.Any ideas?
Thanks, butch h.

O/D lights flashing generally indicate a transmission problem. The only thing other tha a worn clutch/band would be a speed sensor. Does the speedo work properly? The problem with working in low gears is that trans line pressure is real high in lower gears so the pump is working real hard and any slippage that's going to occur in the clutches, and a little does with each shift, is a high pressure grinding. Some of our larger malls/office complexes down here have dedicated plow/spreader trucks, and it's not unusual for them to require transmission overhauls every 15000 miles.