Um, of course you would gain some quickness but you would only go up to 4.10, IMO it really isn't worth changing from 3.73 to 4.10 just for a set of 33's, if you know for sure that you will be going up to 35's then i'd say get some 4.56's now and even with 33's your milage wouldnt be all that bad in comparison but you would be quicker than the average burb.
As for getting them done...it depends where you live. If you are located in a city im sure there is a shop that specializes in gears and drive train. If you are anywhere near Fresno (where i'm at) then the local 4 wheel parts store is a great place to get it done. i had them put 4.88 in my 96 4x and havn't had a problem yet. They even give you the choice if u want premium genuine gear parts or the standard. Also in Fresno is Fearless Gear. PM me if you are somewhere around Fresno for more info