Ram won't shift, please help

Hi, Thanks for all the GREAT info you guys provide!!!! Here's my problem. Truck will not shift out of 1st gear, went to work yesterday and all was fine, went out to lunch and can't get past first gear now. Seemed to come out of nowhere. Manual shifting doesnt have any effect, Reverse is fine. It looks like TV cable adjustment is fine but it seems a "little" sloppy to me but not sure if its normal, fluid is not burnt and was very slightly on the low side (changed with filter

20K ago, 90K on truck now), checked engine trouble light and I get a #37 code but it looks like this usually applies to diesel and I have gas. Ive seen different answers for it and some are trans temp or TCC solenoid or something else alltogether. Light has been on for a while for an o2 sensor but got 37 when I checked tonight. I would really appreciate any help or just a point in the right direction on what to start checking, dont have much time and even less cash. 96 Ram 1500 4x4, 360 Thanks Again, Tom