No Reverse and erratic shift changes

[germarine]

Hi I recently bought a 1997 XLT Explorer that was showing a VSS error (P0500) I was told it is the necessary sensor for the speedometer to work (mino does not). After looking in a lot of forums I found the sensor on eBay and I´m still waiting for it to arrive, but yesterday I had a big issue with the trannie... It got stocked on 2nd gear and just passes to 3rd if I stop pressing the gas until the motor is below 2000 RPM and the I press again slowly and it runs on 3rd but I cannot sense the moment it shifts... Then I had to move back for a moment and when I changed to "R" it behave like if it was in Neutral, no moving, the RPM got up while gasing it but the truck did not move. I turn it off for a While and the I scanned it with one of those 7 dollar bluetooth scanners and it showed an error P1762 and P0102 that were not before, but after starting it again it worked fine. So I reset all codes and drove it for about 3 miles without issue and the errors did not showed up anymore. Next day I was going to run it normally and guess what... no reverse again, it moves very slowly while I stop pressing the brake pedal, but if I press the gas it does not move.
I checked here and on several other forums and some people had similar issues but not exactly the same (none with reverse problems). I found weird that the truck works fine the first miles after I started the first time in the day but then it occurs and the check engine lits, no OD lights on. Any ideas please?