2nd Gen Non-Engine/Transmission 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??