89 lxi automatic transmission shifting

[rrruschman]

I have a 89 accord lxi automatic the transmission shifts fine until you get going about 60mph when you give it more gas and goes up into d4 when you let off the gas and your still doing 60mph then it drops out of d4 and goes about a 500rpm increase give it gas to increase and it again goes into d4 dropping the rpm it seems to me the faster you go it should be like a permanent overdrive but it doesnt are their any shift solenoids or sensors on this model if anyone has any ideas please let me know . Thanks