P0120 & P0755 & High rev to get out of first gear - 99 4runner 4x4 2.7

[cmarandi]

So I have 99 4runner with 163K 2.7L 4x4
the first gear would go too high before it would shift to second. although cleanly. So i learned to drop the rev when it reaches 3000 and the second gear comes in and just don't accelerate fast to get it back in first again. Any ways. rides OK. Highway i lose drive power on hills. a day later hit a bump and the check engine light came on. took it to one guy and he wanted $2700 to rework the transmission. hahaha. i'm not a sucker. took a to a toyota deal and had them do the oil change and give me the codes. The codes were P0120 and P0755. He wans pretty sure the selenoid needs to be replaced and it would range somewhere between 200 to 1000 in addition to the 590 to open the transmassion to see if thats what it is. i said no thanks.
so here is my technical thought:

From the research i've done, the ECM uses the throttle sensor to calculate the flow in selenoid. If I'm getting a P0120, i would think the throttle sensor is sending incorret information causing the P0755 which isfor selenoid malfunctioning.
Im not a mechanic, but i bet if buy the throttle sensor for like 60 bucks at autozone and replace it myelf, (i guess it doesn't need any calibarating) then the high rev issue might get fixed. And then do a transmassion flush to see if the selenoid can get a bit cleaned up and now with the new throttle sensor, basicllay get thing s back to normal.

ANY THOUGHT? PLEASE? I'm not a mechanic!