[KManiac]

Only the electronic, 4-speed automatic (P-R-N-D-3-L) has limp mode and readable codes. There is no band adjustment on these transmissions, either.

Sounds like you have the 3-speed automatic (P-R-N-D-2-1). First of all, check the fluid level. This is most accurate with the transmission hot and the engine idling in Neutral. Top off as necessary but don't overfill. Transmission fluid expands as it gets hot, so what might look slightly low when cold may actually be full when hot.

The transmission contains two planetary gear sets, the front and the rear. Each gear set has a hydraulic clutch (the front clutch and the rear clutch) and a band around each hub (the kickdown/front band and the low/reverse/rear band). The rear hub also has a static, one-way sprag clutch that holds the rear hub. The bands are adjustable. The low/reverse band adjustment is located inside the transmission case. The kickdown band adjustment is located on the outside of the transmission case. The mechanic who changed your transmission fluid and filter should have adjusted the bands at the same time. If they did not, they are a knuckle-head.

Next, try a functional test in each gear.

Reverse - this gear requires the engagement of the front clutch and the low/reverse band. If this gear operates normally, the front clutch and low/reverse band are fine. If not, one is the culprit.

Manual Low (1) - this gear requires the engagement of the low/reverse band and the rear clutch. This gear should not slip during acceleration and provide engine braking when you let off the accelerator. Slippage here indicates a worn out rear clutch pack. No engine braking indicates a loose low/reverse band. Slippage on acceleration and no engine braking indicate both are a problem. Also, low gear, whether manual low or "drive breakaway" low, always makes a distinctive whine that the other gears don't.

Manual Second (2) - In this gear, the transmission starts out in drive-breakaway low. This is engagement of the rear clutch and a holding of the rear hub by the sprag clutch. Drive-breakaway low differs from manual low in that the low/reverse band does not engage and there is no engine braking in this gear. The second gear range requires the engagement of both the rear clutch and the kickdown band. It will shift into second by engaging the kickdown band and hold in this gear. If you have slippage in drive-breakaway low and second gear, the rear clutch is the problem. If low is fine, but second gear slips, the kickdown band is loose. If there is no engine braking in second, again the kickdown band is loose.

Drive (D) - It will start out in drive-breakaway low as above, shift to second as above, then shift to high gear. High gear requires engagement of both the front and rear clutch packs only. When it shifts to high gear, the kickdown band releases and the front clutch engages. If you have slippage in this gear only, the front clutch is the problem.

Now for the quick and dirty:

If the front clutch is bad, you will slip or not engage in reverse and high gear. Replacement of this clutch pack requires a rebuild.

If the rear clutch is bad, you will slip or not engage in all forward gears. Replacement of this clutch pack requires a rebuild.

If the low/reverse band is loose or worn, you will slip or not engage reverse and you will have no engine braking in manual low. Adjustment of this band may cure the problem. If unable to adjust, a rebuild is required.

If the kickdown band is loose or worn, you will slip or not engage second gear only. Adjustment of this band may cure the problem. If unable to adjust, a rebuild is required.

Check your fluid again, do the functional test and let us know what you find.