Here's my experience. I own a 16' aluminum bass boat, fully loaded it weighs about 1600#. That's boat, motor, gas, gear, trailer ect. depending on your boat, i think 1500# might be a tad high for a 14' boat. In either case, you won't have a problem pulling it, even with 3.08 gears.
I have a 98 Ext cab 4.0, auto, 4x4, 3.55's, 265 something Michellin's. i've been fully loaded with gear, gas and 3 people (including myself) and didn't have any problem what so ever. i typically stay around town - 20 miles or so. but it's all kinds of speeds, stop and go traffic, any where from 25 - 55 mph and i've been on the highway about 25 miles going 65 with the boat. not once have i had problems maintaining speed or getting to speed. i also towed in OD, which some people say is dumb, but i did not have any problems with it kicking in and out of OD, and i've got a larger trans cooler with a temp gauge. it never heats up beyond reasonable operating temp. it would never hurt to put a better cooler on the trans, but in this application certainly not necessary. i can hardly tell boats back there, acceleration is fine - tad slower, stopping isn't bad. i can feel that there's something there and i leave extra room to stop. but more than anything, i can feel the back of the truck bounce when going over bumps with the boat hooked up. but it's a pickup and this is expected.
also, i've never needed 4 wheel drive to recover the boat. although i dont drop my wheels off the end of a ramp and i'm cautious about the ramp condition. 4 wheel drive is nice, but i wouldn't say necessary either, just pay attention to the ramp and you won't have any problems.
if you're going to tow 100 miles with the 3.08's you might have to tone it down to 55 mph or suffer a gas mileage drop. but i wouldn't change gears unless you're going to put bigger tires on or tow more weight on a regular basis. my mustang had 3.08's stock and i went to 3.55's and it's such a small difference to be honest it's not that noticable and certainly not worth the time to pull a junk yard axle or pay someone to switch them out. i feel like gears aren't something you want to keep paying someone to switch, it's a little pricey and they need to be done right or they'll whine. i've used 3.08, 3.55, 3.73, 3.90 and 4.10 and switched all around in my mustang. if you were to switch from 3.08, i wouldn't go ANY less than 3.73 cause it's not worth the effort or price for SUCH as little difference.
last summer i took a small trailer, weight rating of 900#, to my cousins house to get wood to build a shed. we built a box that measured 4' wide, 7' deep and 7' wide and filled it with wood. i'd guess it weighed about 950 - 1000# because the leaf springs on the trailer flattened out and frame was on the axle. then i loaded another 150 # or so in the bed. but, i had this huge 4'x7' wall behind my truck that i had to pull home 150 miles. i took back roads and stayed at or below 55 mph and didn't have any issues pulling this either. i was worried that my gas mileage was going to be horrible but i averaged around 16 mph. with the boat i average about 17..
so all in all, the 4.0 is a good little motor and wont have any problems pulling that load. the 4.0 makes pretty good torque down load, and i've noticed its pretty good around 2600-2800. just be smart about where you launch and leave a little extra stopping room. and come to think about it, last year i pulled my boat with my dad's 99 ranger, ext cab, auto, 2wd, 3.0. i could feel it a little more back there than in my truck but still, no problems pulling it. don't worry about towing the boat, worry about how many fish you're gonna bring in.