I'd try putting 4 "stock" tires like 235/75-15" on it and see if it will go any faster up those inclines,after making sure the engine is in tune and breathing ok....33" ones are about 4-5" taller and will "up" your gearing accordingly..make your 3:73's feel more like 3:23's...
My '81 G10 van has a 2:73 rear axle I put in it when the original diff case hogged out the side gear bore--it had 3:08's,and I thought it was doggy with those gears--it'll go almost 60 mph in first now,and I can use second gear to pass going 65 mph (TH350)--but when you take off on an incline its slow,and feels like your taking off in second,or power braking it some!...
I wish I had chosen the 3:42 ratio diff at the salvage yard instead..but the 2:73's they sold me for 20 bucks,no one wanted it and it only had 35K on it...it would be great if I lived in flat open country like Kansas,not so hot here in hilly New England..