Here's why it's likely, but not certain:
* Similar platforms: 1989 and 1990 Chevy trucks were very similar, often sharing the same basic chassis and drivetrain components.
* Same engine: The 350 V8 is a strong indicator of compatibility.
* 4x4: The 4x4 drivetrain should be largely the same between years.
However, there are potential variations that could cause incompatibility:
* Transmission type: While both might be 4x4, there were different transmission options (TH400, TH700R4, SM465, etc.). Even if they're the same *type*, there might be subtle differences in internal components or mounting points.
* Body style: While less likely to impact transmission fitment, significant differences in body styles (like a heavy-duty model vs a standard model) *might* influence transmission selection.
* Minor model year changes: GM occasionally made subtle changes from year to year that might not be immediately apparent.
Recommendation:
Before attempting the swap, compare the transmission part numbers (found on a tag on the transmission itself) of both trucks. A parts store or online database can help you verify compatibility based on these numbers and the year/model of the trucks. This is the most definitive way to ensure a proper fit.
