If pipes are hot then it might be either the blower or the matrix. Can't see why it would be the CH

personally, I can't see it being the head gasket but it might be worth getting a second opinion. it is worth checking the above though, i.e. check the 2 pipes going into the heater matrix to see if they are hot. if they aren't chances are you have a water flow problem

water pump working?

heater resistor ok?

have you got water reaching the heater matrix? is the fan working?

I think they ditched the wiper when they swapped over to alloys

is there a spare alloy wheel on the back. I had to remove my wiper to fit mine on, as the alloy clashed with it. during it's life, someone changed from steels to alloys and when the wheel wouldn't fit they left it in the back!

might be a good idea to not put a pic of your truck with numberplate in your avatar until you sort out your locks! not everyone who looks on here is friendly!

torx55?

should be if its not surging, i.e. if it feels like the brakes are being pressed a bit. worth checking though!

wheel bearings can suddenly "go" as well and like to make a nice crucnchy/squealing noise to let you know!

they tend to break up over time (if not greased up) and make a nice grinding/squealing noise. sometimes they can completely disintegrate making you stop the car to have a look!

universal joints in your drive shafts

wheel bearing or UJ

looks like my wife has been at with the drill in that bottom right corner!

check your engine mounts, exhaust in the the engine bay or even the exhaust manifold. it has to be something that is loose and when it reaches it's natural frequency likes to sing a song!

maybe a dumb question; where are you getting the replacement SMs? i.e. supplier, brand, part number etc also do you also get an overactive SM when starting, like it is still engaged as if the key is still being turned? Just first thoughts!

re the discs, there's a bit to come off before you can get to the disc itself like the caliper and the hub assembly and you may need a big hammer!

up to VIN HA901219 the LR part number was NRC8690, from HA901220 it is STC441

there are a couple of used ones on Ebay including this one: https://tinyurl.com/yaamsm47 plus this one which looks quite smart!: https://dixonfabrication.co.uk/index.php?route=product/product&product_id=90