Maxima Transmission

I have a 2001 Maxima with about 80k miles. I am having some trouble with what I think is the transmission. Engine sounds fine whether under load or not. Drives fine with low/slow acceleration. The problem comes when I give it 3/4 or more throttle to accelerate - the engine revs up to about 3k then stays there and will not accelerate further until I ease off and it upshifts and the RPMs drop. Nissan dealer told me it was probably a bad valve but the whole thing may need to be replaced. Took it to an independant mechanic and he told me it was a cracked cylider sleve - trans was fine. I can’t imagine it is the engine but I don’t know. Any help would be greatly appricated. I dont have a local mechanic that I trust yet.

You are saying that the motor’s rpm will not exceed 3,000 under any circumstances?

Thanks for the reply.
It only has problems under full throttle. In park or neutral it will rev to redline with no problem (odd noise, hesitation, etc). Also, under light acceleration, it has no problem getting up there.

I don’t see how it is a motor problem, so that leaves the transmission - or the system(s) that controls the transmission. Under light to moderate throttle the trans shifts up fine throught all the gears?

Yes, other than 3/4 to full throttle it is fine.