rb25 stutters

[rb20s13]

i just got the rb25 running a month or so ago and ever since its been running great except for when i give it 1/2 to full throttle in 4th or 5th gear it stutters like everything 3 seconds for about 1/8 of a second and it starts to feel sluggish but once i let off some it feels like it free's up and has more power..its boosting fine and i dont have any boost leaks that i know of. In 1st 2nd or 3rd i could hit full throttle no problem with no hesitation. But with my tach (stock ka tach) it stops around 7500 rpm in 1st-3rd gear and the engine just starts sputtering...but my brother who has an rb25 as well he could have his tach go way past that with no problem.Help!

[MEclipseGSX2G]

could be tps?