melabs has replied (yesterday), maybe you didn't get the email.

And nothing you've reported "Points to" DEFINE OSC.
What it does suggest is a problem with your oscillator.

If IESO is 0 then the code fails to run totally. When it's set, the whole thing is much slower than expected.
IESO is the "Internal/External Oscillator Switchover bit".
Meaning that on power-up it starts running on the internal oscillator, then when the external oscillator is running and stable it switches over to that.
If the external oscillator is not running properly, it never switches over.

The default (power-on) frequency of the internal oscillator is 1 Mhz, so with DEFINE OSC 20 it will take 20 seconds to execute a PAUSE 1000. And everything else will run at 1/20th speed too.

You say that you are swapping between a 2550 and 4550.
The pins are different. Are you sure you have the crystal and caps on the correct pins after swapping.
On the 2550, it's pins 9 and 10. On the 4550 it's pins 13 and 14.

The 2550 only has one VDD pin and the 4550 has two. Are you connecting both VDD's.