my 2000 started doing the same thing AFTER i got larger tires...went from 265/75/16 to 285/75/16 and the shift pattern seemed off...took it in, local shop said the computer needed reset to the larger tire size, take it to the dealer..so i did, they reset it for the speedo change (which was insignificant to me, nor did i care about that) and i got to talking to the mechanic who informed me that basically he sees this all the time with larger tires: the tranny/rearend are geared for the factory sized tires, when you put larger ones on, it throws off the "ratio" and causes the shift pattern to go up, it also wont go into overdrive when it should, and he said this will/can eventually KILL the tranny..i asked what to do?? he said nothing short of changing out the gears, going from say a 410 to a 390 would fix it.....i find this VERY hard to believe...has anyone else ever heard of this???