Rear End

so i have a b2200 with a small block 350 with a turbo 350 but it has the stock 5 speed rear end and when in drive doing approxametely 60 mph its reving at almost 4000 rmps. My question is if i were to put a rear end out of a 2200 with an automatic would it help with my over reving problem?

I don't think that would fix your issue, I believe the gear ratios are the same. It could be your transmission. Does it have overdrive?

The automatic and standard rear are the same ratio.
You're going to have to upgrade your transmission to a 200-4r or a 700r4, to take advantage of an overdrive.
You might also consider swapping a GM 10 bolt, for gear availability, because there is little to nothing available for the Mazda rear.
Not to mention, the Mazda rear will die behind a 350... I have killed three of them!

Both rears have the same 3.90 to 1 ratio.

An overdrive trans will bring those rpm's down if your willing to spend about a $1000.

The easier way to bring down the rpm's is by using taller tires.

What size tire you running on the back?

Thanks to: baha, sincitylocal, and oo7bob!!! You gave the exact information that i was needing. I had already known about the overdrive with the 700r4 and with me handicapped be best idea. Was just hoping the standard trannsmission rear end would be a different gear ratio then the automatic.....But now i know. Thanks again fellas
Happy Truckin.