Reason I ask is while cruising at certain speeds, for example 45 my car shifts out of 4th to 3rd constantly with steady throttle. Also at 35 it shifts into 2nd to 3rd to 2nd again.

FWIW the car is a 1998 Civic DX with about 160,000 miles on it.

 

I think its all ECU for a 98. My 95 has a cable you can use to influence the shift points.
Maybe your ECU is getting bad sensor data (MAP sensor?).
Pure speculation. I think the Helm manual has a tranny troubleshooting chart/guide.

 

See if this helps:

 

Hmmm Im not to sure what symtom that qualifys as.

 

If you're driving right around the speed the shift point is at this is going to happen. You can't adjust the shift points on that trans at all. It's purely electronic.

 

Hmmm, it never used to, I can understand if i was giving it more throttle, or going up a hill, but on flat ground with a steady foot it always staying in a gear.

 

trans fluid level?
how long since the last service / fluid change

 

The fluid is right at the top of the full line, the fluid looks dark. I have no idea when the last service/fluid change has been. The car is new to me..from the looks of it, maybe it is the original fluid?

 

Definitely change/flush that fluid, at least a few drain/refills. If it looks dark on the stick then it's really burnt or filthy. I've flushed fluid where the stick still looks pink and dark brown mud came out during the flush.