94 Honda Civic Auto Tranny problem

I have a 94 Honda civic EX with 144k miles. I bought it and later found out that it has been sitting for almost 3 yrs. When I drove it at first it shifted just fine and had no problems but about 10 miles into the drop home it felt like it slipped and about 2 more miles it slipped into the false neutral and i couldn’t get it to go in any gear but park until i shut it off and turned the car back on. then it would go into the gears just fine for a few mins before doing it again.
So i changed the shifting solenoid and the lock up solenoid. i also changed the transmission fluid then test drove the car which would go a lot farther than before but would do it again after awhile. At about 60-65 mph it drives fine, but once I hit the first red light it slipped out. I turned it off for a few seconds then fired it up and it shifted into gear just fine. After driving a while, it will start throwing a code 4 (Crank position sensor). I experienced a general loss of power. i just can’t figure out what else to try or if i should just get a new transmission for the car. I checked to see if there is a difference in shifting in gears so I shifted through d4 to d3 and there seems to be no issues there.

To sum it up, I’d like to know if it is a component I could fix myself(or even just test) or a whole new transmission is in order. Thanks in advanced! 🙂