I'll say I haven't had issues with stickiness or difficulty shifting when it was cold out, but I imagine in warmer temps, the non detergent SAE 40 would work too. It may not sound as ideal as some other fluids, but it is what Spicer spec'ed for their tranny and such and it is bronze safe. Only downside is the tranny and transfer case will get quite a bit warmer on long drives especially at the top end of RPMs. The t-case lever is usually my indicator how warm the t-case is getting and it will be hot like a cup of coffee cruising at 60mph or above, 55mph and below, it's pretty warm but not hot