engine problems

when i hold my throttle at one position to maintain a speed, it sometimes bogs out, but a steady bog, it kinda erratically pulses like a really wavey powerband but at one rpm, its quite hard to explain, you also could kinda say its like my brakes are being lightly applied randomly and sporadically as I try to maintain a speed on level ground, I have an 86 B2000 with a lot of the vacuum shit removed, its been rebuilt 90,000 km's ago, but a lot of the original stuff has 344 000 K on it, so I know something is going or gone but I dunno what, I already checked my carb choke, my distributor, ( it had little oil under it but it didnt change anything when i cleaned it off), i rechecked all my old plugs in the removed emissions stuff, and this stuff has been removed for about 200 thousand k so i know its not that, any other possible ideas? i drive my truck deliverying pizzas daily and its really pissing me off, should I get a webber carb? i hear those make your truck run insanely better and smoother, oh it runs so rich it smells like a boat from time to time also. and webbers are aropund 800 CDN were i live so i dunno if thats a good option, sorry for the novel, but ive asked everyone and no-one can really help me!!!