Kinda hard to diagnose without DTC's and your description is a little unclear. Not sure if you have 3rd gear or not but the last sentence makes it seems like you only have 1st and second gear. This can mean the transmission can't shift (only change from the 1,3,5 clutch to the 2,4,6 clutch).
Possible causes...
- Lose battery cable(s). Make sure they are good and tight.
- Lose ground(s). Check all the ground wires for corrosion and make sure they are tight. There are 2 on the left side of the engine, one just left of the engine on the frame and a cluster of them under the driver seat.
- A malfunction with shift solenoid 1 and/or 2. These are behind the clutch cover assembly so you can't check the connectors unless you remove the cover however the most common cause is a wire harness connector not fully plugged in. If the battery cables/grounds do not solve the problem, check the Linier Shift harness, there is a 12 pin connector somewhat hidden under the crossmember just behind the engine (just below and in front of the sway bar). Make sure all the wires are correctly inserted into the plugs and it is fully plugged in. There have been several instances where a wire was not fully "engaged" into the plug causing various problems.
Not a very good pic but this is looking back...
View attachment 280721
If you can get the DTC's, I can walk you through the diagnostics if you want.