Gearbox Problem :(

[Shhtuart]

It struggles and hold revs and change gears after about 25 minutes of driving. Gearbox is sweet up till that point so im praying its something else.

[Bennoz]

Does anyone have a spare fuel pump lying around or have a cheap one for sale?

Yeah I've got a few spare...

[payaya]

Black oil that smells burnt can only mean the internals of your gearbox slipping causing extra heat which causes black oil that smells burnt.

You may notice the new oil may start going black again straight away.

Judder when taking off and seems like there is a judder in between gear changes? Hissing noise?

Do a torque converter test.

You said it shifts 100% in tip? Even when hot?

This might be a long shot but give your mas and connector a clean.

But given that it's not going it when hot would suggest when you let your gearbox cool down the debris in your gearbox is settling to the bottom of pan and when it heats up it's loosing oil pressure because the pump is getting blocked up.

Another prob ca be your cooler lines are blocked but most common is the oil pump crapping it which gives similar symptoms to what ya getting.
It's not ya fuel pump!!

Everyone has copped what you have with an auto. I have twice which was a rebuild each time.

[Shhtuart]

Just an update, after 2 weeks of sub 30 degree heat, my car didn't play up once.

It runs extremely well when its cool or warm but I noticed my voltmeter was reading my volts as 13.8v when it's cold but when it starts heating up it drops down to 12.1v. I was sitting in a drive-through yesterday and it dropped to 11.8v which I know isn't right.

Am I right in thinking that when the car is running with nothing on (radio, AC, etc) that it should sit at 14v?

So, this brings me to my new theory, the alternator is slowly dying and something inside it is failing at high temp. When the engine bay cools down it runs fine until it heats up again. When in auto and its playing up it struggles to rev high enough to change gears at the optimal range (when slowly accelerating) but when i put it in tip i can change it up gears prematurely and it goes to the next one but still struggles to get revs enough for the next gear.

Would a failing alternator would prevent the car from revving high?

The battery is a 4 month old 440CCA which is fine.

Thanks for any input, it's 19 degrees today so I'm fine for the time being

[payaya]

The charge of a battery drops as it heats up. Check the tension of your alternator belt and don't worry about it IMO.