Skipping Third Gear

I have a problem with my recently rebuilt tranny.
If I drive aggressively it runs the gears fine, but if I drive like I normally do it almost seems to skip third gear and bog down into 4th. It had a code for the park/neutral switch but that went away when I replaced the TPS, MAF and Plenum with some junkyard parts and hasn't returned.
I just want some ideas on what I can do without spending too much more money. I was thinking one of the shift solenoids was sticking, but I am not sure how to check it.

You need a scan with a trans function scanner to look at solenoid commands and gear ratio errors also make sure you have good vacuum to the modulator if so equipped. Always post the year also.

That's my fault, it's a '93.
I will give the modulator a look and get back to you. I am not sure if my mechanic friend has a trans scanner, but I will ask.