[TECH]: Power loss @5k rpm?

ok. so i finished putting my car back together after replacing the broken timing belt. compression about 180 across all cylinders. set the initial timing, started it up. ran real rough, and i noticed a clicking coming from (i think) the fuel pump relay. then the rpms would drop and the car would stall. this was at idle to 2000 rpm. so i set the timing at the distributor, and the car runs great (woo hoo!). drove around gentle for a while until i was confident everything was ok, then punched it. very smooth up till about 5k rpm, then the rpms abruptly dropped, like the engine cut out momentarily, then caught again. at the same time, i heard the clicking in the same relay again. it's reproducible at 5k rpms, every time. also, when i coasted down a large hill in 3rd gear the same thing happened but between 3k-4k rpm. any ideas? i'd suspect a fuel problem, but since i've been messing with so much other stuff i feel like it's something i've done wrong. could it be a timing problem? i didn't readjust my idle mixture after setting the timing and idle, but why would that make my relay click? otherwise the car seems fine; my noisy lifters are even quiet now for some reason. weird. any help, as always, would be greatly appreciated. i feel like i'm sooooo close to having my car back.