17,400lb weight for the P-38J/L is with the 50 gal fuel deduction for take off and warm up. 17,699lbs is with 410 gal fuel and pilot full internal capacities for fuel, oil, ammo etc.
take a look at the rates of climb for P-47D, F4U-1, and P-51D and you will see they are 2,000fpm for the P-47D, looks like 2,300fpm for the F4U-1-FG-1, and what looks like either 2,400fpm or 2,600fpm for the P-51D under the same conditions as the 3,200fpm of the P-38J/L ie military power.