38's is pushing a 10 bolt front hard even with chromo's and HD ujoints. In certain terrains they can take bigger tires but is depends on terrain and drving style.
A 10 bolt rear even with chromo's is going to be pushed very hard by 37's. The front axle can take more tire because it usually sees less of the trucks weight. The rear axle tends to take more abuse and even a beefed 10 bolt rear isn't going to take alot of heavy punishment for a long time.
The fronts take less weight and abuse and can handle bigger tires for longer times. Stock axleshafts can usually handle 35-37" tires for awhile depending on driving style and terrain. Chromo's in a 10 bolt make 38's more possible and maybe larger in certain enviroments. Chromo's just help insure less breakage and the ability to drive a little more aggresively.
The problem with upgrading a 10 bolt to chromo's is that the area of breakage just moves to somewhere else like the ring & pinion gears, lockers, locking hubs, or driveshaft.
If you don't already have alot of money invested in your 1/2 ton gear it is cheaper to upgrade to stronger gear that will take more abuse from big tires.
Harley