Hard to start and sometimes will not start at all when cold

For the hard starting issue, I would suspect a fuel pump wearing out. S series trucks with the 4.3 are notorious for bad pumps, and in my experience every mile after 150,000 is on borrowed time. Borrow a fuel pressure tester from AutoZone's loan a tool program and check the pressure. It needs to be a minimum of 60psi to start. Here is a how to guide:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

As for the 4x4, there is a vacuum driven actuator under the battery tray. This actuator engages the front axle. It is a common problem for them to dry rot and leak. You will have to pull the battery out and remove the tray to see it. Also look at the vacuum line coming from it. As a matter of fact, you might want to inspect all of your vacuum lines, as they are old and dry and could be collapsing under pressure or just plain leaking.

Vacuum leaks: https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Here is GM's test for fuel pressure. A bit more convoluted than our test, but I wanted to give you options.