TRANSMISSION

Hi,
Am Eric Alis Keynesian I have experienced some problems that my mechanic seems not to understand seemingly because the same problem recurs.
Now, last year 2016, check engine lights came and after a series of diagnosis, the mechanic recommended we change the throttle as well well as the fuel pump and the computer. (Am not well versed with mechanical terms). The problem at the time was solved. However, for some time now I have noted that;
1. When I drive at rev below 2000 rpm and mostly with slight acceleration, upon reaching to a place where I may need to accelerate, the car does not pick. As in even when pressing there is no response at all. The pedal seems like it is dead. However, when I stop and switch off the car and on again, the problem is resolved and I can continue with my journey very well unless I again drive at low rev/speed (2000 rpm).
2. The second problem is that when I drive for very long distance say 170 km non stop, the car starts to behave in a funny way like when pressing the accelerator, the rev starts to go backwards towards 1000 rpm and the car sound like it is being choked. At the same time, if I still force it to move, gears engage in a funny way such like jumping some gear numbers hence the car "limps" forward. To solve it, I have to stop and switch off the car for like thirty minutes and then continue with my journey.

i recently did diagnosis with a mechanic and it had the following error codes
CODE 001; P0132 A/F SENSOR1 (B1) HO2S1 (B1)
CODE 002; P2138 APP SENSOR
CODE 003; PO731 1GR INCORRECT RATIO
CODE 004; P0732 2GR INCORRECT RATIO
CODE 005; U1001 CAN COMM CIRCUIT.

He cleared the codes and upon rechecking there were no error code. He then proposed we change the who gas pedal mechanism of which I am reluctant when I remember the trial and error I saw mechanics doing. Kindly advice if it the right move. I have no mechanical background and the same problem has not been resolved
Thanks in advance.