94 SW2 Appears to go into low when at 70 mph

For a while now my 94 SW2 automatic transmission w/180k miles on the
body and 90K on the engine & trans will rev high 3.5k to 4k at
approximately 70mph. If I pull over it drops down as I slow down and
will be OK for a while. If I stay at 55mph it doesn't happen. I know
it is low gear because I simulated it when I put the car into low and
it is identical. Also the check engine light comes on and then off. I
am trying to schedule an appointment with the transmission shop but
thought perhaps this has happened to other Saturn owners. I replaced
the tired leaking valve tapping engine at 150k when the trans stopped
going into reverse. I spoke with the trans shop and it could be a
cheap fix or up to 5K in a rebuild. I will just get another trans at
6th Planet Auto in FL where I get all my used Saturn parts if it comes
to that. This is my favorite car ever and I want to keep her.
Thanks Linda

PS Which computer reader is a text (not lamp) readout for my 94 that
anyone recommends?

 

The trannies performance is linked to engine performance so if the
engine is not performanic well and is taking a higher throttle setting
the tranny wil downshift out of OD and shift to drive which yours
appears to be doing. I would focus on engine performance and related
sensors and not tranny at this time.

 

Agreed, but with one qualification: the OP does not mention having checked the
transmission fluid level -- and since that's *very* simple, that should be the
first step. And if it hasn't been done recently, I think I'd change the
transmission fluid and filter too. It probably needs doing anyway, and it sure
isn't going to hurt anything.