So your power goals are very similar to my own. Your post doesn't say and the Autoguide ap doesn't show signatures if you have it listed so I'm going to assume you have a 4R100 automatic transmission and not a ZF 6S-650 6-speed manual which would need nothing much more than a clutch upgrade.
The 4R100 can be a perfectly competent, if not brilliant transmission for your power level. In stock form, especially if it has 215k on it, it will not survive for long behind that power level regardless of the ancillary upgrades you perform. The stock torque converter will not handle the power well either. Heat from the additional power will be a significant problem but is easily remedied with a 6.0L transmission cooler and a deep sump pan. It would serve you best to not install this items until you upgrade the transmission.
For myself, I plan on running an aftermarket billet converter with a slightly lower than stock stall speed of about 1800-2000 based on the intended torque production (my stock converter stalls at 2400rpm now with a tuned stock engine) and increased lockup clutch capacity. A proper 4R100 built with the upgraded parts to handle up to 1000lb/ft of torque, good clutches, upgraded hard parts, possibly a BTS valve body, a deep cast pan, and a 6.0L (03-07) transmission cooler.
Now, the transfer case on the 4wd models just needs good clean fluid, in 2hi you'll never break it, but drag racing in 4hi is another thing all together, and you might just want to have a spare on hand.
Driveshafts are often overlooked. Take more of the stock driveshafts on some of the newer trucks like the 2014 Ram, and they're running 5"+ aluminum prop shafts to the rear. I'm not saying that's necessary, but that's the horsepower and torque level you're attempting to make and they have a margin of additional strength engineered into the driveshafts on the new trucks as well. At the bare minimum, you want to invest in new heavy duty universal joints, a new carrier bearing, and minimally an inspection, cleaning, and lubrication of the slip yoke, possibly replacement if wear dictates it.
The axles should be fine, again, service them with high quality fluid. Replacing the bearings probably isn't necessary, but they should be checked for condition and properly preloaded for used bearings. It never hurts to check the emergency brake components and rebuild them if needed. Same applies to the front axle, only with the hubs and ball joints being the components to pay attention to.
Good luck with your pursuit of power. Keep us updated with your progress.
Sent by my right thumb!
The Current Truck (Oct-2013 to Present):
1999 (Early) F-350 Lariat, CCLB, SRW, Black/Tan
7.3L Powerstroke, 4R100, 4x4, 3.73, 37x13.50-18s, '05 Axle Swap, 6" Fabtech lift, GTP38 "D66" turbo upgrade, SCT 4-position chip with custom tuning by me, Straight Piped 4" down pipe through 5" dual stacks, N-Fab full length triple steps, Pro-Tech cab guard and tool box, louvered 5th wheel gate, Hella 500 Fog and Driving lamps, much more to come...
The one I'll miss, (Mar-2009 to Jan-2014):
2000 Excursion XLT 4x4
6.8L V-10, 4R100, 4.30, 285/75-18, 271whp / 388wtq
The one I won't, (Jul-2005 to Sep-2012):
2005 F-350 XLT, CCLB, SRW, 4x4 FX4
6.0L PSD, ZF-6S650, 3.73, 35x12.5-18, 4.5" Lift