So I just finished putting 4:10 gears in my 99 f-150 4x4. 4.2 v6, manual tranny. blah blah blah.... I have a problem. I took it to the ford dealership to get the speedo re programmed and they said the lowest it would accept was 3.55, and so we did that and told the trucks ecm that i had the smallest tires it would accept to trick it a little more. It helped a little but now when my speedo says 70 mph, I am actually going about 65 mph (thanks to mr. gps) I dont care that much but I was wondering if there is anyway to further fix this. Oh yeah I run 265/75/16 tires on the street and I dont care what it says for my swampers (36") cause thay are only on for off-roading. Thanks again. Also before the tire size trick thingy the speedo said 70 mph when i was going about 58 mph.

 

Re-post this in the chips section. I'm pretty sure Mike from superchips can correct for any gear size and also tire size using a superchip or programmer. Unfortunately you will have to buy the product. Probably the best would be the programmer since it will allow you to change the program when you have the SuperSwampers on. That is important since the speedo is directly associated with shift points, timing ect.
I am not sure if the programmer has been released for the v6 yet but again, post in the chips section for more information.

 

thankyou, i am such a NEWBIE.