07 Mustang V6 Convertible Automatic transmission slipping upon acceleration

get new transmission oil and replace it completely (that means no top ups ) u have to drain all of it . This happens when your valve body gets choked because of old oil which becomes thick for it to push normally that is y when u press the accelerator pedal it gives pressure to it and it start to push the oil with force

First thing to check is fluid level. If fluid level is ok you can do this simple check to look for excessive transmission wear. Take a clean white cloth and wipe down the tranny dipstick. You should see the pinkish red color and you will notice some brown to black debris on stick as well. If you notice excessive amount of residue you have significant internal wear. You didn't mention how many miles on your car. You have to remember that in a tranny with considerable wear if you change fluid you could make the slipping worse. This is due to the lack of particles in the fluid. In a worn tranny the particle create more friction to help tranny engage. When you replace fluid the oil is now more "slippery". This will cause even more slippage than you originally had.

Also should have mentioned you might have a plugged filter causing the tranny to starve for fluid. This is also a result of excessive wear ie., particles plugging up the filter.

1st thing to check is fluid level also make sure right fluid for your car

ALSO TRY SMELLING YOUR TRANS DIP STICK, DOES THE FLUID ON IT SMELL "BURNT"? TRANNY COULD BE STARVED.

Problem with all the aforementioned advice above... THERE IS NO DIPSTICK ON THAT MODEL