Hello and welcome to JustAnswer!
If the engine is running fine yet it takes a high amount of throttle to get the car to move then either the transmission is slipping, the brakes are stuck or there is a mechanical failure in the trans.
First check the trans fluid to make sure it's full, also note the condition.
If the car does push when in neutral then you've ruled out a mechanical issue with the trans being locked up, and you've ruled out the brakes being stuck.
If it does roll in neutral then the problem is in the transmission. It could be a slipping clutch or low line pressure due to a pump failure, sticking regulator valve or a plugged filter.
Thanks for the prompt and informative reply.
The transmission fluid in the car is extremely clean.
The pump is probably an expensive item.
Is the filter a metal screen ?
Is the regulator valve and option for me to fix. I can drop the pan and change the fluid. Will this give me access to try to resolve the regulator and filter?
The filter is a normal fiber type.
The regulator valve is in the valve body. The valve body would need to be removed and disassembled to get to it and see if it was stuck.
Is it possible the Transmission Solenoid is bad ?
Also the regulator is in the valve body, is that exposed when the pan is pulled ?
I did notice one thing with the pan dropped. This transmission has a cable in the front which works freely and seems to engage it. There is a cable on the throttle which seems bound up. It is connected with a set up like a string light you would have in your basement, with the silver adjustment balls. What operates the cable on the front drivers side of the transmission ?
Any chance it could be the Torque Converter ?