Engine dies out - HELP

I have an '89 5.0 5-speed Mustang with 124K miles on it. Under full throttle acceleration in first gear the engine dies out somewhere above
3,500 RPM. It almost feels like a rev limiter, valve float or fuel starvation. However, if I cruise on up to 5,000 RPM at a bit more leisurely pace, it runs fine. It's only under full throttle and only in first gear that I've had the problem. What's up?
Some additional background; 3.73 gears, full aftermarket exhaust, K&N fender mounted cold air kit, 1.7 rockers, underdrive pulleys. All air and fuel metering components are stock and original except for an aftermarket fuel pressure regulator. TPS setting was verified today at .997 volts. The long block is stock and original except for the 1.7 rockers. I'm still running the original fuel pump although the fuel filter has been replaced.
Thanks! Dave
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Dave Wick wrote:

First thing I would do is pull any trouble codes from the computer. Looks like the problem is occurring while the engine is at a high demand for fuel. It could be a bad fuel pump, clogged fuel filter, improperly set fuel pressure regulator or even clogged injectors. Also, check the fuel pressure to see if it is within spec at idle and when the problem occurs.
It could also be something wrong in the electronics (MAF, TPS, IAB, various sensors, distributor electronics, etc.) but for me those problems are difficult to detect and that is where I take it to a good mechanic.
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Dave Wick wrote:

My first guess would be a bad fuel pump. It's hard to test for that, because you need to check the pressure while it's under a heavy load. After 16 years and 124K miles, I'd just replace it.
--
.boB
1997 HD FXDWG - Turbocharged!
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