I would go 9x28's>9's keep the 4.10's and get a purpose made converter that flashes to at least 3000 for a 383, that 1800 verter is killing your 60/ET. Your mph/weight shows you are using around 307hp of whatever hp that motor is making which should be 350+?, its just not being allowed to unleashed itself early enough...you got a low 12 potential car there.