[A/S] increasing gear ratio in tow vehicle

[zuzaberra@xxxxxxxxx]

Hello everyone--

I am pulling my 23' Safari (loaded about 4500 lbs) with a 92 Chevy 
conversion van, 3/4 ton 5.7 350 V8 engine. It has a tranny and oil 
cooler. 

I've noticed on hills and grades I have a hard time.  On a long, 
medium grade in PA I had the accelerator to the floor, and could only 
reach 55 mph.  I asked the dealership about my rear end gear ration--
it's 3.43.  I think that is too small.  I'm worried about crossing 
the Rockies with this setup--I don't like to worry!

My question--can I just buy a new gearset and have my mechanic put it 
in?  I can buy a 3.73 or a 4.10 rear end gear for about $200 online.  
If I do this, do I have to change anything else--the differential, 
for example?  Does one thing lead to another?  I'd like to keep this 
van as my tow vehicle, but if it's simply the wrong thing and I've 
made a mistake, then I'm willing to cut my losses and buy something 
else.

Any suggestions?

thanks,
Susan