* Same engine: The most important factor is whether both trucks have the same engine. Transmissions are often engine-specific. If the '88 and '89 trucks have different engines (e.g., a V6 in one and a V8 in the other), the transmissions likely won't be interchangeable.
* Automatic vs. Manual: An automatic transmission will not fit in place of a manual transmission, and vice versa.
* Minor Differences: While the transmissions might be largely the same, there could be minor differences in mounting points, bellhousing bolt patterns, or even the length of the output shaft. These small differences might require some modification or the use of different parts.
* Specific Transmission Model: Even within the same engine type, there might be slight variations in transmission models (e.g., different gear ratios). While generally compatible, double-checking the specific transmission model numbers (usually found on a tag on the transmission itself) is recommended to ensure a perfect fit.
In short: It's *highly probable* but not guaranteed. Before attempting the swap, carefully compare the transmissions and verify compatibility with a parts diagram or a mechanic experienced with these trucks. A simple visual inspection might not be sufficient to catch all potential issues.
