I don't recall if there are any factory recommendations. I'll have to check the manual later.
Experience has shown that shifting so that the rpms when the next gear is engaged are around 1500 seems to yield the best fuel economy. That works out to shifting up at around 2200-2500.
First gear is pretty short in these cars so the 1st to 2nd shift usually works out to around 2500 and then lower for the remaining gears.
Although the engine has lots of torque, even down low, acceleration is a bit lethargic under 1500. When you hit ~1900 (the torque peak) it really takes off.
Some people who have "chipped" their cars report a heavy shuddering that feels like lugging between 1300-1500 rpms under heavy load. This may be an awkward stage in the engine's fuel map and not true lugging. I generally avoid that rpm range under heavy load since it's well below the torque peak and not very productive.
Typically, I shift low for best economy when I'm putting around town but will stay in gears up to 4,000 rpm for best acceleration when merging onto the freeway from a short on-ramp.
Hope this helps.
