[72c20customcamper]

Cheapest would be gear change. But at maybe 1 and 1.5 gallon increase in milage and driving you say about 5k miles a year it's going to take a long time to recoup. My 85 k20 has a 700r4 and 3.21 gears . I'm looking to put either lower gears or a 400 in it . I dont use od because if I hit an incline even at highway speeds the trans hunts. I get almost the same mpg in od as I do in 3rd. I had it looked at by my trans guy and he said nothing wrong with the trans and it looks to have all the upgrades .