Well I bought the truck and had some issues with smooth shifting. On the recommendation of this site I ordered a few bottles of mt-90. I dumped it in and noticed a definite improvement but once it gets warm and I have to shift down into 1st or 2nd the gears still grind a bit. I did notice when its cold outside or the truck is not hot yet it shifts perfect.
I was thinking perhaps there was a thicker fluid I could use for this warm Florida weather that would work like when its cold outside or the truck is cold.

 

Sounds like the synchros are just a bit worn. Does double-clutching help the grind?

By putting a thicker fluid in it you may compromise adequate lubrication of everything else, kind of like putting SAE50 into a worn motor to damp out the clatter.

Give the MT-90 a little time or try Amsoil MTG, both are excellent and exactly what your trans wants to operate well.

 

Yeah is this something that might get better with time? I replaced the bushings on the shifter and also took the play out of the clutch. Its not horrible but damn the thing shifts so good when its cold. I can shift down with no issues even into 1st gear. Just thought maybe I could get something different in there that works in this heat.

 

Let it work it might get better. Stupid question are you rev matching on your down shifts? If not that will help you down shift a lot smother. Hope this helps