86 Nissan pickup problems

I have a 86 Nissan pickup with the Z-24 engine. It idles good, and runs good but in a situation where I need passing power or 5th gear up a steep incline it falls on it's face. If I ease into the gas, it does fine, but I need more power.
I 've changed fuel filters and new plugs. It has more power but still collapses under a load when accelerating.
This is the ugliest truck I have ever seen but I have nothing into it and love driving it. Great everyday beater!
I appreciate any suggestions :dunno:

a major nissan problem is chocking have you cat replaced and put a free flowing muffler like magniflow or flow master if you can find muffler shop that carys them Fullbores they are the same as magniflow and flowmaster but at half the cost and if you have the pipe end right after the muffler you'll have a killer sound to the truck even little street racers will wonder trust me also ad cold air induction to the motor mor power and after thats done go find a mustang gt blow his doors off and and you 'l gain speed up hill and try down shifting to forth untill thats all done but your problem will be solved

Keep in mind this truck only has about 103 hp off the lot new.

Is this an 86.5? Z 24 tells me it probably is. Did you change all 8 spaek plugs. Yes 8. If it doesn't have 8 it's not a Z24 and maximagirl is correct, If it is Z 24 it's 134 hp, and a pretty zippy little engine when running correctly.