loud chatter in higher rpms

hey guys i drive a 5 speed 87 mazda b2000 ext cab i gotta preatty loud chatter after about 2800 rpm or so in every gear not that exact rpm but usualy around there. once that chattering starts im losing all power (not that it was fast to begin with.) I adjusted the valves the other day and even went a little bit tight around .10 i know the stock gap for them is supposed to be .12 right? i was told going just a little bit tighter it quiets it down but it didnt. its way louder when im driving then if im parked with the clutch in reving.

for memorial weekend i took the truck about an hour out to the lake and on the way honme it was a bit warmer and my truck kept feeling like it was kinda like gasping when id put my foot on the gas like it was losing compression or trying to die until i would take my foot off the gas.

so far i have replaced the fuel filter, adjusted valves and put a muffler on (the old one rusted completely out)

its got a little more go but high end still just falls on its face. any help would be awesome guys thanks.

Noises are really hard to diagnose without being able to hear them.

Is the noise coming from under the hood, or from the back of the vehicle?

Maybe a differential is out of gear oil, or a bearing is going bad.

Maybe a water pump.

"its way louder when im driving then if im parked with the clutch in reving"

yeah i guess a better explanation would have been good haha i didnt realize i left that out. its kind of a chattering knocking sounds like real bad valve chatter but only happens in higher rpms kind of a knocking. i am actually starting to think its probably my throw out bearing. im gonna check that out more but any sugguestions are greatly appreciated so thanks for the input man.