3.1 lopes during idle

Hi all. I picked up this 1998 Monte Carlo LS with a 3.1 recently. It ran really bad when I first got it. 180,000 miles. I changed the spark plugs with the recommended GM ones and cleaned out the throttle body real good. I cleaned the IAC and changed the Idle Position Sensor. A huge improvement. I fixed a couple of vacuum leaks and overall, it runs pretty good. But one thing is it is hard to start. It always starts, but you have to crank it for 2, 3 or 4 seconds before it actually takes off. And when it does start, it does not start with authority. It sort of starts slow and then builds up to normal idle RPMs. When I stomp in it, it takes off like a bat out of hell. I checked the fuel pressure and it is around 41 PSI when idling and goes up when you hit the gas. The other thing that is weird with the way it runs is when I'm sitting at a light. I first come to a stop at the light and I swear you can't even tell it's running. Just as smooth as can be. Then, as time goes on, it starts to waiver a couple of 100 RPMs up and down. Then it gets into the loping thing, where it starts tugging on the brakes. It never stalls, and suddenly smooths back out and is fine again. Occasionally, there is a slight hesitation when I hit the gas, but not always. I was wondering if it could be the EGR, or the MAF. Any ideas? Thanks.

Do a full scan first and look for pending codes or misfire counts, there are a lot of things that can cause this.

I thought I'd stop by and just let you know that I changed out my injectors yesterday and it seems to have corrected the problem. I tried running injector cleaner with the gas and it got a little better, but was still acting up. Now she starts quick and idles smooth.

What kind of injector cleaner did you use?

What kind of injector cleaner did you use?
I ran two 20oz. bottles of Chevron Techron in 12 gallons of gas.