Late model, by late model generally pretty much anything after 1990, gearing has a tendancy to be something on the order of 30 - 31 mph per 1000 rpm. 70 at almost 3000 rpm is in the order of 23mph per 1000 rpm.
The automatic should be a 4 speed with a lock up torque converter. Although the torque converter is genrally only locked up in 4th it could be locked up in any gear but most probably if not 4th, 3rd and 4th. The locking up action I think of as a reduction of about 500 rpm but in the saturn it is probably closer to 300 rpm. I'd have to go and pay attention to mine to figure that out.
Bigger and heavier cars tend to be about 500 rpm.
Think of the function of the lock up as a splitter if you will or an overdrive. Using rpm in 4th (top gear) as the basis for the thought.
Once in 4th, final drive has a tendancy to be 1:1 with over drive being usally about .75:1.
That way when shifted to overdrive, your cruising speed would remain the same but engine rpm would reduce to a lower rpm thus improving gasoline mileage.
Any torque converter has slippage, so when it is locked up the slippage is eleminating reducing engine rpm at the same road speed improving gasoline mileage. When accelerating or climbing hills it would unlock, engine rpm would increase improving power. When the need is done, it locks back up.
Heavier cars it is easier to see this watching the tachometer. 'Specially if you are using cruise control.
I can see this watching the tachometer on my 94.
The gear shift selector has or should have something like a D1 and a D2 with normal driving done in D2.
D1 starts the car moving using 1st gear with shift points to #2, 3 and 4 raised a bit to compensated for hilly driving with a heavy load or brisker acceleration.
D2 starts the car moving in 2nd gear. This gives better fuel economy.
Lock up torque converters were first used around the early 70's across the board. Chrysler some where around 1975ish and not on all transmissions.
The first use of lock up that I am aware of was the Packard Ultramatic designed in the early 1950's as a 2 speed transmission with a lock up torque converter. Also used by Nash and Studebaker when they bought Packard V8 motors and transmissions around 1955 and 6. Problem prone and short lived.
You should be able to sense shifting when starting from a dead stop in either D1 or D2 by seat of pants and then the lock up take place. The tachometer should also tell you.
Also if you have the computor scanned, error codes should come up indicating that a gear was not selected when required.
It kinda sounds like it is not shifting into 4th however that also could be the lock up not working too and probably that has the higher probability. Again at o-dark-30 I am not going to go and look but with mine on cruise at freeway speeds, it does not have enough power to pull the almost 7% grades at 70+ miles an hour and it down shifts instead and it sounds like it is trying to wrench the engine out of the mounts when it does it. Assuming the lock up function emulates an overdrive, 24mph per 1000 rpm + 33% a general assumption of overdrive gearing functioning = 31.2 mph per 1000 rpm. Seems to equate to the lock up not working. In that case it might just be a wiring problem to the electical connector for the transmission or something in that area.
It might also pay to have the transmission serviced if you have not had it done. I do not drive mine all that much and the shifting has had a tendancy to be a bit sticky from disuse untill I get a few miles on it.

 

Hi. Welcome to the Saturn forum. Great bunch. I have owned my 99 Saturn Sc2 since 2006, and I must admit I LOVE these cars! I'm definetly a Saturn freak. A cold air intake works really good on the Saturns. 99sattieSC2

 

First if you have a question make it in a new post in the proper area. Don't attach your questions to other posts.

2900 rpm's at 70 mph is normal with the stock diameter tire of 195/60X15

http://www.miata.net/garage/tirecalc.html