The vacuum lines that the persusder pointed out are usually easily broke but being that your 4x4 light is on I doubt that your lines are broke... where he has pointed out where your actuator is there is a wire right the that is the 4x4 light switch is. Also in that area is where you'll find the front drive shaft connects to. If you vacuum line is un hooked or broke your 4x4 light would not come on (at least when mine broke it didn't) He was also talking about your heater controls not workung right and if you are standing in front of your truck, on the passenger side by your engine oil dipstick there is a vaccum line that goes down by it beside the intake manifold. There will be a tee with a black plastic line going to it from the firewall. Coming off the tee there will be a white plastic line coming from it that goes down to the top of your transfer case. If you follow the front drive shaft back from the front you will se that it connects to the transfer case. Where that white line connects to is an actuator switch with a square rubber plug with for plastic line coming out from it. (Blue, green, white and red) the blue and red, those vaccum lines going to the actuator on the front axle. The ones in the pic... The white is the supply and the green one comes up beside the trans and comes up out on the drivers side by the brake booster reservoir next to the intake and has a check valve ont the end of it. If any of those are crack or broken your cruse control wont keep speed and your heater when you excellerate will change to defrost or to vent... but as soon as you let off the pedal say if you has it set to heat, it would go back. I would check those lines and look at the front drive shaft and go from there... Sorry for the book...
