I have a 2004 4.0L 4x4 supercab with 299k miles. I love my truck and I know it will need major repairs before long. I'm prepaired to buy a new engine and transmission to have put in it, just not aware of what all that entails.
What specific engine is in this truck?
what specific transmission is in this truck?
What should I keep in mind going forward?
Is it more economical to rebuild instead?
Any and all advise is appreciated.

 

Expect 4k for a totally "new" engine from big name sources, could be less for some local place to rebuild what you have. I have less to say about transmissions, haven't even asked about that on my 4.0l sohc as mine seems happy with 175xxx on it (changed it at 125k when I got it) .
If you want it staying tight and good replace front end bushings, keep good shocks in it, check all grease points and maybe change your diff oil as it's overwhelmingly overlooked

 

Price isn't an issue. I found a new sohc for $2700. Not sure what install would cost. I'm trying to go around buying a new vehicle.

 

They always say to be ready to swap intake / manifolds from your old engine to a replacement engine so your vehicle's wiring plugs in correctly.
The truck's "computers" need all their familiar sensors live.
I've read it "takes a day" to pull and swap an engine in our vehicles. I bet this assumes someone knowledgable has ordered up any necessary gaskets etc. ahead of time.
I believe you want quality parts used on any rebuild. Genuine Ford tensioners and timing chain assemblies are ALWAYS STRESSED by people who know.
Get the equipment listing from a dealership (run the VIN). I bet you have a 5R55E transmission. At 300K I bet it's smart to do a full (hard?) rebuild while it's out of the vehicle.
Do you use your 4WD much? Should someone in your position at least open the transfer case?
Even if you were to reuse your transmission I believe 300K on a torque converter is time enough.
Maybe lay out / buy a transmission cooler? Do you tow or plan to?

Would sending your radiator out to be tanked and tested be smart or would replacement be smarter? I don't know.
Would replacing your heater core be wise? Possibly. How's your coolant looking?

Don't go for any junk exhaust manifolds. A pal got just 2 years out of cheap "mail order" manifolds for his F-150.
I'd want stainless steel studs 'n nuts for my exhaust if possible.
I suppose replacing engine mounts is part of this job.
Send your shafts out for a balance and new unis?