The L99 engine does have Active Fuel Management. Depending on the conditions, it can be V8, V6 or V4 and comes with an auto trans. The LS3 is a straight V8 and straight drive. You get 26 more horses with the LS3. The all have torque management in the PCM but that can be taken care of by a competent tuner. I agree with you, a sports car should have a manual trans. The L99 engine is no slouch though. Whatever you buy, you can't be wrong. Welcome to the site. I won't hold the Marine thing against you, even though I'm ex Army. Thanks you for your service and good luck.
Imperial Blue Metallic/2SS/M6
In My Hands: 12 November 2009
2004 Joe Gibbs Silverado
2000 Pontiac T/A (RIP) 1 November 2009