I have a ford 555d backhoe that acts like it is down shifting or going in and out of low range while driving forward does not seem to do it in reverse. I do not believe it has a low range only gears 1-4 shuttle shift. Filter has been changed strainer has been cleaned correct oil has been added 3 times zero time to me 5hr and at 20hr. At zero time strainer was clogged allowing very little oil causing trans. to slip. At 5hr strainer had 3 little slivers no slipping at all. The strainer on my 20hr was a bit more then I would like but at that rate it would take aprox. 200hr to clog the strainer no slipping what so ever. She takes of in 4 gear just fine a little week on hills is my thoughts. All dump switches disabled all accessible plug and plug pins cleaned and have batt voltage going through them when in forward or reverse. My thoughts are it seems electrical some times its a very fast in and out of low to high range for a lack of better term. At first I thought a shifting fork was slipping in gears 2 - 4 but its happening in 1st gear there's no lower gear than 1st on this machine (as far as I know). Rpms don't seem to sky rocket when its happening just seem to slow down and then I will put it in neutral pop it back in gear and I'm back at normal operating speed again maybe for 20 sec maybe for 1 min. In 1st it seems to go in and out really quickly higher ranges once it happens I have to put it in neutral to fix it. Sorry for this being so long thanks a lot for any help.

had a 555 backhoe with the 3 speed hydro, acted same way, turned out it had fins in the torque converter that were variable pitch and had locked in the high speed range. don't know how you would check it, might get hold of a ford dealership to find out