This is about a friends Tacoma 2002 V6 with 5 speed. He's got 30K miles on it and did a gear oil change from stock Toyota oil to the Amsoil 75-90.
He's been driving for 2 days and reported very hard shifting almost grinding between shifts. When cold, 1st gear can only be selected when completely stopped. Before he could roll to a stop and already select 1st. The gearbox had no such symptoms up to the oil change. This behavior doesn't change much even when the truck has been driven for while and the oil is hot. He's a responsible driver (actually I'm not so sure about that)and takes care of his truck.
Does anybody out there have similar experiences?
Thanks for your input

If it's GL-5, get it out of there asap. The GL-5 additives will eat the soft metal in the transmission (ie synchros).

Replace with a GL-4. I'd strongly recommend Redline MTL or MT-90.

It is a GL-5 spec. The Toyota service manual states GL-5/ hypoid oil. How is it possible for the GL-5 to eat the syncros right after the fill and test drive? It shifted hard right immediately and didn't change much when warm.

My truck has been doing the same thing. Butter smooth until I changed it with 75-90 synthetic. Now first and second gear give me issues.. especially first.. I can feel it grind sometimes and I have to wait till it's at a complete stop when cold. Once warmed up, it is fine..

I dont know why..

It obviously won't harm them right away, but over the long term it's not good for them and will do damage.

Roger Brown, aka 4Crawler, has some good info about synth lubes in the tranny on his site.

yeah, why in the heck toyota says you can run GL5 in your tranny is a mystery...definitely not good.

It's often mystified me as well - but I think the reason is, in dino oil GL-5 will work ok, won't eat the brass all that fast (if at all really), and is easier to stock at the dealers'. Stocking multi-grade oils is a high cost proposition. Don't we already complain about dealer costs passed on to the consumer?

The problem tends to emerge with synthetics. Watch and see if nearly every complaint occurs after someone goes synth, after running successfully for years on dino GL-5. Synths are more 'slippery'; the shear strength and lubricity prevent the synchros from grabbing the gear cones. Even some synthetic GL-4 oils are too slippery for the synchros, ask me how I know!

If going synth, by all means pay close attention to the grade: use GL-4 exclusively. Redline manual transmission gear lubes have proven highly successful in getting older trannies to shift like new. Better than new really, freshly rebuilt trannies often don't shift all that great until the synchros break in.

I checked out Amsoil's website.. it's wierd.. in one section it says to use GL-5 and a few lines below that it says GL-4.

Wait till you read the owner's manual / FSM and it says either will work! Don't you believe it, at least when it comes to synthetics.

Ford friction modifier is reputed to work as well, but its stinky stuff and personally I would have an aversion to it...

I think if you research more, you will find Amsoil is too slippery. I have had Redline MT90 in my 98 5spd now for 60k miles. Great. Also in my 88 5spd for 40k miles. Redline has something to help the snychros that Amsoil does not.