03 Mustang GT 4R70W trans help!

[Motox852]

Ok guys, the transmission in my supercharged 03 Mustang GT is out or going out, car sometimes wont move in any gear, sometimes it will barely. Leading up to this, the trans temp gauge has been reading up to 250 after about 30 minutes of driving, sensor appears to be good yet its been doing this for awhile as the car gets driven maybe twice a month and goes to the track about 5 times a year. Fluid was bad and burnt so I changed fluid, filter and flushed and made 2 decent drives around town before it started slipping again and just barely got the car back home as it just didnt want to move. Currently I have a FTI 3500 stall converter thats a year old and Im hoping its still good, but now that I need a transmission, Id like to know the best option for a new upgraded 4R70W that will be capable of handling around 900HP? Want to go ahead and have the right transmission as I prepare to do the engine build later. I was thinking about going with a ATFspeed stage3 built 4R70W and use my FTI 3500 converter. I want to make sure my converter is still good as I hear they seldom go bad, but dont want to put a possibly bad converter back in a new tranmission. Thought? Thanks!!

 

[Deleted member 38176]

250 is EXTREMELY hot the 4R. Are you not running aux trans cooler? I ran my old stock 4R on my old 2V (550rwhp) with a big trans cooler and temps never broke 200 even while running at the track.

On my new setup, I had the tranny rebuilt with a Suncoast Stg 1 kit and a GIANT tranny cooler. I am just shy of 1000rwhp and the tranny is running strong!!

The BIGGEST enemy to an auto is not so power, but heat!

 

[Motox852]

250 is EXTREMELY hot the 4R. Are you not running aux trans cooler? I ran my old stock 4R on my old 2V (550rwhp) with a big trans cooler and temps never broke 200 even while running at the track.

On my new setup, I had the tranny rebuilt with a Suncoast Stg 1 kit and a GIANT tranny cooler. I am just shy of 1000rwhp and the tranny is running strong!!

The BIGGEST enemy to an auto is not so power, but heat!

Yes I have a cooler, now I have added a 2nd one and also 2 cooling fans so hope this helps keep the new tranny cool. I thought I may have a bad temp sensor but it appears to be working fine that I know off.