Ok, here are some tips:
The P-51 is fast, real fast, with great visibility. But in the Jabo role, there are better planes out there.
My favorite jabo ride is the F4U-1D. You get the same bomb load-out plus 2 more rockets, and its easier (and safer) to aim rockets than to divebomb. 8 rockets will take down a vehicle hangar. If you miss a rocket or two, the F4U-1D's six .50cals can finish the job. The F4U-1D is also more durable than the Mustang and less prone to being shot down by ground fire.
Runner up would be the P47D (the silver version). 10 rockets, 3 bombs, 8 machine guns. Its a single engine bomber.
Compression is the leading cause of death in new guys doing jabo attacks. One way to avoid this is to chop your throttle as soon as you go nose down. I also like to drop 2 notches of flaps, as the sound of the flaps being retracted automatically when you start to get fast acts as a sort of overspeed warning claxon.
When you go in on your run, make sure you release your bombs first, since they weigh more than rockets. If you try a hard pull-out with a pair of 1,000 pounders on your wings, you're liable to self-destruct. Also, if 1 bomb hits and the other misses, you can bat clean-up with a rocket or two and use the other rockets against any ground vehicles that might have upped to defend the field.
When attacking a fresh field, I leave my bombs at home and just bring the rockets. My first run over the field is to take out the flak. The next run is to fire the rockets without worrying about flak. Or, if your target is the vh, then strafe the vh flak on your initial run-in and fire your rockets as you fly past the hangar. You should be able to kill the flak and take down the hangar in 1 pass. After this, work on taking out the AA guns near the runway, then take out the guns at the city (if there's a base capture imminent, otherwise just leave them be).
Don't do a hard pull-out after your run because you'll either pull off your wings or loose too much speed or both. Extend out with a long, sweeping climb to conserve your speed.