I've never had problems with T5's.....then again i've never made a massive amount of power. From talking to the last owner, he blew up the T5 in my GT at about 80,00 miles and the "new" one has lasted now till 135,000 (i believe) miles and still feels great. The one i had in my '84 5.0L lasted 155,000 miles until i sold the car.
I'm sure that the one in my car won't last long since i'm using it with slicks and i'm about to install ported GT40 heads, B303 and nitrous within the next 6 months or so....or until i get to the track i should say.
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2005 Suzuki Hayabusa GSX1300-R
1980 Ford Thunderbird - 255 V8
ported heads, 5.0L ported stock headers, O.R. H-pipe and Flowmaster 2-chambers, dual roller timing chain
hi-po Mack Truck hood emblem 
1985 Mustang GT 5.0L T5, F-303, GT40p, headers, off-road h, flowmasters, MSD stuff, etc.
Sold 02/06/04 
1989 Mustang GT ET: 13.304@102.29 mph (5-24-03)
Sold - 1998 Mustang Cobra coupe, 1/4 mile - street tires: 13.843@103.41 (bone stock)
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