Hesitation Problem
 

Got an 87 N/A with 140k on it just rebuilt the heads and car ran great for about 2 months. Then one day it just started boggin down when you get on it a little. If you drive slow then she runs fine. But it causes a problem getting on the highway for example. Does it in all gears. Usually at low rpms around 1,500 to 3,500 rpms. When you give throttle slowly in neutral no hesitation. But if in neutral and give throttle pretty quick it kinda sputters a little before leveling out. But under any kind of hard load it doesn't have any power and just stays at the same speed kinda like starving for fuel right before u run out of it. Already checked fuel pressure 27psi at idle and around 35psi with throttle open. Also idles at a constant 1,000 rpms. Any suggestions?