transmission gurus, i have a fairly urgent problem

[vortec]

my c1500's 4L60e was running fine, last night, but on the way to work, today, it started shifting way late and having huge dead spots where it almost felt only slightly better than being in neutral. the fluid level was well within the acceptable range, but i picked some up, anyway, and added it. not much change. it doesn't seem to be going into overdrive, for one thing. i limped it to work, and think i can make it home, if i drive it conservatively, but, it's my dd, so i need to figure this out, soon. i won't have a chance to get under it until tonight, but being armed with some ideas and opinions could help. thanks

[76GMC1500]

Pull the pan and check the filter to make sure it is not plugged.

[southerner]

Check your vacume modulator and vacume line for any leaks or disconnected hoses.

[lt1s10]

sounds like you have a computer problem, so you need someone with a scanner. if the filter is not stopped up then its not much you can do, without checking for codes.