The stock rear will be fine if you swap to an overdrive transmission. The easiest swap would be to use the factory 3 speed with the Borg-Warner overdrive, it's a direct bolt in. You can usually find them for around $150.
The next option, if you want to stay manual, would be to use a T5 from an S10, which would get you the overdrive gear. That swap has been covered numerous times. try doing a search for "T5 swap" to get the specific information.
Going automatic will require an aftermarket adapter, either from Langdons or Buffalo, as the 235 will not directly bolt up to the modern overdrive automatics.
