Vehicle will not Move and code P1791

We own the car listed above (vti v6). When we bought it the engine light was on and is still on. We have already replaced everything underneath and also the cars fuse box the whole thing because first thing last year when it got cold out the heater fan would not work. So changed the fuse until it blew the whole box. So we replaced that along with the blower and it worked until now. Lately have been experiencing some issues. It has been rainy and cold where we live and I had gone through some puddles in my driveway and I had noticed that sometimes it had been hard to turn the wheel when not going fast. Next day it was around forty degrees I let engine warm up for ten to fifteen minutes then put into reverse it would not go without a lot of gas. So we parked it and bought Actron pocket scan plus and it gave us this code of P1791 which is the TCM. I do believe that it is probably corroded with dirt and my husband is going to check that tonight after work. Also, look for the thing inside to see if it is corroded. I had also noticed last week that when the snow melted off the roof the sunroof must be leaking because it was wet on the window and wet by the fuse box on the passenger floor. Maybe that has something to do with all of this too. Anyway we really need some help fixing this. Now today when I tried looking inside the driver side for the thing I am supposed to see if it is corroded or burnt I could not find it, sure I will have to pull off some plastic to see it, but so I started it to see if anything had changed and now the service engine now light is on and so is the loss of power light on the dash board. So I waited for all the beeps as we always do and then started it. At first it stalled out then would not move at all. Put in to drive would not move, tried all the gears and nothing stuck in place. Can you please send us all the schematics of where to find these sensors in the engine and inside the vehicle and how to do this repair? Sincerely Andrew and Heather