Stock HP is 345. The stock transmission is marginal in the first place. If yours is still original (not been rebuilt) and with that many miles, you might need a transmission rebuild in the not too distant future. Adding 125 HP to my 03 SS with a Radix Supercharger, caused the stock transmission to wear out at 70k (installed the supercharger at 2,500 miles). That should give you some idea about what you can expect from the transmission.