Working on bugs..advice please

[Cbrianroll]

Hi all. 2001, 4.0, auto, 4x4. 132,000miles. New to me…bought to be a firewood truck but my son wants it so I’m making it better hopefully. Current state, no brakes, they will be here next week, that’s easy to do. This is the stuff that isn’t as my troubleshooting isn’t the greatest. There are no check engine lights on/flashing etc. engine has a little fluctuating up and down at idle, amp gauge needle moves up and down a little too, dash lights dull and brighten in rhythm with it. I’m assuming time for an alternator, but wondering if I’m wrong since the motor is doing the fluctuating too. I have yet to pull plugs to check condition as the weather has been bad. It has a new battery, volts were 17+ when running. Advice is appreciated.
Next, transmission, only got one long drive in an the front brake was sticking and getting hot so will check more after new brakes but it only shifts when you let up on the gas and at upper speed I noticed the overdrive light was on and said OD off? Or on? I forget but I assume it is an issue. Fluid appeared high on the stick when warm, in park and idling. Filter and fluid will follow next week also but advice on issues is appreciated.
Lastly,,if there are any quirks I should know about I would appreciate it also…it is a work truck but need it safe and running so I don’t have to tow it lol.
Thank you all for reading and your patience with my rookie needs…

 

[alwaysFlOoReD]

17+ volts is much too high. I think your voltage regulator is kaput, and that is in your alternator. I'm not sure how easy it is to replace but some research should help. That might fix your idle problem.
Voltage should be regulated to 13.5 - 14.5 V.