Idiot lights or real issues?

my check engine light has been on since i bought the truck (97 f-150) with codes bank 1 lean and bank 2 lean. the manifold to y-pipe studs were broke on both sides so i thought they may have been on due to the large exhaust leaks...........exhaust was fixed and i took it for inspection. it passed and the service station never mentioned anything.
well about a week ago my light on the shifter handle started flashing. the one that says overdrive off. it seems like as soon as its started and drives off it shifts late out of first gear. the rpms get pretty high before finally shifting. after that it shifts pretty smooth. but that hard shift triggers the light to start flashing. not sure if its some kind of warning light for the tranny?
the check engine light is on sometimes and off sometimes. today it started flashing. i never saw a check engine light flash before. do they ever flash?

O/D Lights flash = Bad transmission (normally)
... Sorry.

great......... and now on the way to work today it was very jerky. the tach kept dropping very sharply. almost to zero at times. almost like the truck was dying. is that also tranny? i assume since the tach is connected to the engine it wouldnt be tranny related. possibly some wet wires? its been very wet and rainy the last 3 days. not sure the last time it had a tune-up with 225,000 miles on it

Have the PCM checked for codes. It should have a P07XX code in it. You might get luckyn and it be just a solenoid or a wiring problem. Please post code numbers back here.

took it to autozone and had someone help me that actually knew something for once! had it scanned and 3 codes
0320 crank sensor condition
0300 cylinder misfire in random cylinders
0401 egr system fault

the guy at autozone was a big help and we pretty much narrowed it down to crank position sensor. i got under there and the mounting tab was broken off so the sensor was able to move anywhere it wanted...........hopefully the drive to work tomorrow morning goes much smoother! 10 inches of lake effect snow on its way...........