Originally wanted to tow a 3000lb (optimistic weight) boat/trailer with my 2003 2WD 4 cylinder Taco. In reality once the boat was loaded with gas & gear, it probably would be at or over 3500lbs. Another issue I was concerned with if I was involved in an accident and the boat was above my Taco tow limit, should I have had the rig on the road to start with.
As mentioned in the above link, also considered installing lowered ratio differential gears, too. Another concern was getting the boat out of the water with a 2WD with manual transmission & stock gear ratio.
In the end purchased a lighter 2000lb boat/trailer. My 2003 2WD Taco with stock gears handles this boat easily in all situations so far. I'm sure it could handle a heavier boat rig on the road, but unsure how it would handle pulling the heavier boat out of the water with 2WD. A 4WD would be a great advantage pulling a heavier boat out of the water.
If a boat was within my towing capacities and I had a 4WD, would try pulling this boat out of the water before making the purchase with the owner present or get with a friend that has the same size boat and try pulling his boat out of the water.
Just a thought!