Sounds to me like thinner oil is a possible problem then, since the oil is thicker cold.
Wouldn't be a bad idea to call as poster above anyway.
Other 833's work fine with 80-90 like you had so there may be a condition that Brewers knows why yours does what it does.
Sounds like normally worn synchronizer rings to me. (the colder thicker oil stops the gear quicker than the ring does with thinner oil) and the ring is what is supposed to do it.
