Abs Problems

[odieub]

ok here goes my truck is a early 01 was drum brakes 4.10. swapped to a disc rear was 3.54 then ended up selling my drum rear and was going to swap front gears but ended up swapping rear gears with my old stepdad that has a a 97 4.10 truck and wanted the 3.54 from the rear. ok he swapped the gears an everything run fine no problems speedo worked fine till the other day i done a big 4th gear burn out till about 4k (i have a 215 12v in here too) and the abs/brake came on . shut off started back up no lights, ok a fluke i drove for 2 weeks and all fine. then i run it up to 100 mph and when i let off of it the abs light poped back on but speedo never flickered. could there be a piece of trash on the abs sensor?? or something more i don't mind fixing anything but hate throwing parts at it and cant stand for lights to come on and the brake pedal stays the same when this happens?? any ideas guys??