Have you tried moving the light closer to the basking spot, or the basking spot closer to the light...?
It only needs to be that hot on the basking spot on one side of the cage...
I don't know, it just seems you're using an aweful lot of wattages and bulbs for a rather small tank...
I have one 100W bulb on the basking side of mine's tank, and one 65W bulb on the cool side, both store baught, regular old clear light bulbs in heat clamp lamps. Basking on mine stays 98, warm side is 87 a few inches away from the basking spot...
Got a picture of the full set up?