4x4 chevy k10 1973 drifts in lane alot, hard to stay in lane on bumpy freeways...any advice on what to repair?

2wd is when the hubs are turned to the 'free' position, and the t-case shifter is in 2wd. It is 2wd so long as the transfer case is in 2wd even if the hubs are turned to 'lock'. All the hubs do is lock the front axle in.

It is up to your transfer case to supply the power to the axle. So when your t-case is in 2wd, and your hubs are locked, the front axles are turning but have no power going there, which simply reduces fuel mileage. 4 low is for low speeds 4 Hi is for faster speeds- but the hubs must be locked to have 4wd.

Since you have locking hubs you can also have 2wd in low range giving you extra power at lower speeds (think burnouts) by shifting your transfer case to 4 low, and hubs to free.