engine bogging down

[77 cc lb]

hey everyone. i have a chevy 292 i-6 and it is giving me some trouble. after warming the engine up and starting out on a trip the carb starts to spit and sputter when i step on the gas and after a certain speed like 35-40 the trans seems to downshift/upshift. would that be vacuum leak or possibly the trans modulator? did some research on the modulator and the exhaust does'nt blow smoke, so i'm thinking it is a vacuum leak. i sprayed wd-40 around carb but could'nt hear or see anything. if any one is familiar w/ this engine or have vacuum diagram, i would appreciate any info. thanks