LSx Alternator and 4L60E Problems

[78bronzechariot]

I just got my 4.8 Vortec (LSx)/4l60e running on Thursday. It has been running well, but the shift points seemed close together. I took it on its first long trip (two hours) one way today. When I got back home and was parking the truck, I had it in reverse and idleing for a few minutes while I was talking to my fiance. Then the check engine light came on. I plugged my code reader into it and it said P1810 TFP MANUAL VALVE POSITION SWITCH - CIRCUIT MALFUNCTION. I have done some looking and it sounds like the computer can't tell what range the mechanical selector is in. Has anyone had any problems with this, and what the fix is?

As for the alternator problem, When I go into wide open throttle either accelerating or to force a downshift to pass, my voltage gauge drops down to 11.5 and the headlights dim. I drive a mile or two and it comes back to 13.8. Is the alternator about to give up or is there something I don't know about like a cutoff at a certain RPM? I had it tested at the parts store and naturally it didn't do it then and tested good. Any other thoughts on the matter?