The car's gauge is stuck at 3500 RPM at a stop or while accelerating.

It could be several things. The worst thing you can do to any car is let it sit. What you need to determine is when it shakes, does it seem as if the trans is slipping or does it feel like an engine miss. If the check engine light is on, you should have the computer scanned to identify if there are trouble codes that will direct you to the problem. Most parts stores will do that for free. Once you determine if it is the engine or trans, then you can attack the problem. Also, if it sat that long, you need to make sure the fuel is new and I would recommend a good injector cleaner. Things can get gummy from old fuel.

If you notice it when it shifts to 2nd, it sounds like the clutch pack to me. However, a bad torque converter can cause problems. As far as the check engine light, it should be accurate regardless of the tach.

There are so many parts in these vehicles anymore that can cause problems. Please keep in mind, I'm trying to give you the best answer I can based on your description. It could even be engine related. For example, if you have a weak fuel pump, it could lose power after the pressure drops.

See if you can confirm that it isn't an engine issue too.