Transmission fluid

[sixxdeuce]

when the weather is warm and ive been driving for a while my tranmission gets stiffer and likes to grind gears more often. Its a little stiff and notchy when i first start it up in the morning, but then it does fine for a while and then after a 45 min drive or so it starts giving me problems again. It just has regular valvoline 75w90 gear oil in it now. Do you think some redline oil will help, on their website it says it helps in cold weather but it seems like mine has problems when it gets warm. what vicosity are you other socal guys using for this climate?