I'm making a couple of assumptions here to fill in the blanks.
1. It's 2wd.
2. It's 5-speed.
If those are correct, you really ought to upgrade to a later transmission. You can get a transmission from an '86-'95 2.3L (4ZDE) Isuzu pickup, and use the diesel front-half of the case (we call it the bell housing, but it's really the entire front case) on the later-model gas transmission. It has stronger internal parts, and should outlast the truck. In my 9 years of scavenging, I've only run across one 5-speed diesel transmission. The gas ones are much more common, and are usually available at self-service yards for around $100. I've pulled several later-model gas transmissions, and I haven't even gotten every one that I've seen. The same transmission can also be found in the 2.3 gas Isuzu Amigo, and the '86-'89 Isuzu Impulse. Some of the Impulse transmissions have a higher 5th gear, which makes it quieter at highway speeds.
If you search for one of these, you have to make sure it's not from the 2.6. That's a completely different transmission. I checked the inventory at Pick-n-Pull for Isuzu Pickups within 20 miles of Dallas. There were two. I think you should be able to
see the search results here. Keep in mind, these trucks could both have the wrong transmission. I doubt there's any way to know without checking it yourself.
Jack
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'83 Isuzu P'up Diesel LS - Original Owner
JoeIsuzu@IsuzuPup.comIsuzuPup.com