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Is the '89 a fuel-injected truck? If so then yes, the tank should foit the '95 just fine. If the '89 was a carbed engine, however, then the hole in the top of the tank for the fuel sender assembly to drop in will be too small for the in-tank fuel pump that the '95 has.
Then there is the matter of which tank you're replacing - rear tanks are most 19 gallons on the 3/4-ton trucks so that's a go, but the front ones can range from 19 gallons for the 2wd trucks down to 16 gallon for the 4x4 trucks (with them the transfer case gets in the way of the longer tank) and swapping a short one where the long tank was is not a direct bolt-in...