I have a chevy that has a loss of power and stalling.

About a week ago I drove it and it would spin the tires over, but the next day it wouldn't. it could be bad gas the truck was in the shop for about 6months getting the tranny fixed and I put gas from a gas can in their that could of been sitting outside

I can crank it and it will idle fine normally takes 2 tries to crank it 1 with a little bit of gas for about 3s then it will crank the 2nd time 1-2s. I noticed when i crank it that white smoke comes from the exhaust, but i can't say if it does that everytime. When it stalls if im fast enough i can give it gas to keep it going.

I'm going to change the fuel filter tomorrow or the next day but I don't think its been changed in awhile because the bolts on it are pretty rusty. I've replaced wires/plugs.

could it be the distributor? I had a dude a few weeks back from look at it and he changed the timing a hair.

Maybe backpressure/cat?

Also when I press on my brake fully when I release it my engine will rev up very slightly. Vaccum leak?

Any help would be amazing and greatly appreciated

Also I cranked it once and heard a hissing sound (vaccum leak)? but the thing is it only made the sound once and i havent heard it again