I really appreciate anyone who takes the time to read this and help me out, im stummped on this...

I have a 2003 silverado 5.3 4L60E 90000 miles and recently have been experiencing transmission problems. The transmission slips in every gear but only under half to 3/4 throttle. When i give it full throttle it wont slip, however it doesnt want to shift. I was thinking a filter at first but since it doesnt slip at full throttle that doesnt make sense. Fluid looks good. Also when i take off "normal" it will slip for 2 seconds, grab for 2, and just keep going back and forth. My current idea is there is a bad connection somewhere because for one, it started right after i went through some deep water; and two, one of my brake lights is only half as bright as the other (which i dont know if it would be related or not, but its still a bad connection somewhere) I have no transmission codes, just an O2 sensor code which ive been meaning to replace.

Any ideas?

I suppose i can also mention ive seen the tranny run 130 - 150 degrees and when stopped ive seen it hit 170

A normal code reader will not ready transmission codes. You need something like the Tech II scanners the dealerships have. Most transmission shops also have scanners capable of reading transmission codes.

I would start by changing the transmission fluid/filter. This may address the problem, but will also give you a chance to see if there is any metal in the pan. After that, I would take it to a transmission shop and have it scanned for codes.

you check the fluid stick to see if it looked like it had water on it? light could have gotten some water in it, try removing it and see. remove the bulb from the socket and inspect for water/corrosion or could also be the ground for it

High RPM would increase flow/pressure to the bands, low RPM would decrease flow/pressure to the bands. Which is typical of either a clogged port or low fluid or a clogged filter. Start with the fluid/filter as Roy has suggested.

Well, just completely lost second gear yesterday. I guess it is worn out. Rebuild kit on the way! (not that i feel like pulling the tranny...)

Anyone else besides me think its the common sun shell gear? All the grindings from the gear could clog the filter and cause slipping in all gears, but when the gear sun shell gear does go, you lose 2nd, 4th and reverse.

The sun shell or gear good be it. Mine just went out on me recently, but when mine went, it was a given. Truck slammed into reverse, then when in forward gear slammed into second then second disappeared. The ring where the gear slides in completely busted off of the sun shell. In this case maybe the splines are stripped away on one or the other. I would remove the tranny and dig into it so you can get all the parts you'll need at once.