01 4WD Blazer, 4L60E.
Just had my transmission rebuilt a couple thousand miles ago and I've been noticing that when I'm somewhat heavy on the throttle it won't shift to 2nd until like 2700-2900 RPM. But if I'm light on the throttle it'll shift normally at around 2000. I called the guy who rebuilt it and he said to try replacing the fuel filter because that could of been a possible cause. Did that and I'm getting better MPG now but still not fixed. He also told me that all the shifting was controlled by the computer. I don't know much on transmissions, any ideas or thoughts?

 

The PCM commands all transmission shift points, however, if the engine is not running properly, the shift points will be affected. The transmission is much like a computer: If you give it bad information, it will give you bad information in return. In other words, if the engine runs poorly, the trans will shift poorly. Is the SES light on? If so, what DTC's are in memory? Have you checked fuel pressure and leakdown? If so, what were the results? A harsh 1-2 shift can also becaused by a sticking 1-2 spool valve in the valve body. It's more common when the trans is at operating temp, (30+ minutes of driving time) and rarely happens before that.