I'll give you the benefit of the doubt Lawhoops...

If you're 6'3 and benching 400 pounds then you are going to have to give up theweights and focus on generating handspeed above all other things.
With handspeed comes timing so I'd recommend using the suspended speedball (floor to ceiling) a lot, a little on the regular speedball but that won't come off straight away, it takes time to get that one right, and also punch only the ligfhtweight bags, not the heavy bags until your technique improves.
Speed speed speed for you Mr Lummox, right about now you probably have the turning circle of the titanic after all those years of pushing metal.
Secondary, work on flexibility, stretch regularly and practice twists. Make sure you can flick your hips each way so you can generate your power from down low.
Lastly, roadwork and skipping for the stamina that you will require. I said roadwork, not frickin treadmill, those treadmills are a waste of time. Find a good hill and use it regularly. Also do shuttles twice a week for sustained speed bursts required in the last 30 seconds of every round.
You'll need your respiratory wind to be at a high level for when you start to spar with another human being.
Because if you haven't been sparring before you will find out very quickly that it is nowhere as easy to hit an experienced opponent as it looks on the tv or in a video game.
Your stress/tension levels will increase markedly and your breathing will tighten so the fitness and stamina is crucial.
You will get hit. Probably quite a lot.
Take it on the chin. Keep your hands up and remember to breathe.
Don't fill your pants and never show up again, and don't get angry and go spacko or they will ban you from returning. Keep your hands up and your eyes on your opponent.
Remember muscle in the weights gym is little help to you in the ring.
Take your time as you have a lot to learn.