Lagging acceleration

Well, I bought my 2000 blazer 4x4 over the summer. It needed a new transmission, so I had a rebuilt one installed. I also noticed the gas gauge did not work. I was also experiencing lagging when i first started the blazer, like it would get caught at about 1800 RPMs, and if you would floor it, the engine would lag really bad. After running for a bit, the lagging would go away and be fine the rest of the trip. I took it back to the transmission shop and they said that it was the fuel pump that was bad. After replacing that, my gas gauge works, but I am still experiencing the lagging acceleration. Any suggestions on what could cause this problem? Thanks

Well, I bought my 2000 blazer 4x4 over the summer. It needed a new transmission, so I had a rebuilt one installed. I also noticed the gas gauge did not work. I was also experiencing lagging when i first started the blazer, like it would get caught at about 1800 RPMs, and if you would floor it, the engine would lag really bad. After running for a bit, the lagging would go away and be fine the rest of the trip. I took it back to the transmission shop and they said that it was the fuel pump that was bad. After replacing that, my gas gauge works, but I am still experiencing the lagging acceleration. Any suggestions on what could cause this problem? Thanks

How about a full tune up? How many miles?

Plugs
cap
rotor
fuel filter

Tune-up could easily be an issue, especially if you havn't done one in a while, but if your only getting lagging at certain times and not others, my advice would be to get it on a scanner, check and see if anything comes up(pending codes) etc, and go from there.