Ford Repair: 1989 Full Size Bronco, shifting gears, filter service

Question
I drive a 1989 Full size Bronco, 351W with a C6 3 spd automatic transmission.  Here recently it has started shifting late, reving up to higher rpms before shifting gears.  I tried adjusting the modulator which made it shift easier, but did not make it shift sooner.  It is driving fine, just shifting later than it used to.  Any ideas on how to make this go away?

Answer
Service the filter. The bands inside the transmission probably need adjustment. A shift kit might make the problem go away. Although, the shifting between gears can sometimes be harder with a shift kit. Additives like ATF Stop Leak condition the seals outside but more importantly inside also. So throw in a quart withe the filter service. By no means do you ever want to ever over fill the transmission.