I have plently of pressure at the tub pout but when I switch to the shower , it's very little pressure. It's not the shower head because it's low without one on.

Describe your diverter set up. Is it an diverter spout or do you have a three handle valve? Back to you, Tom

Back to the same question.
Describe your diverter set up. Is it an diverter spout or do you have a three handle valve? Let me know, Tom

Spout

When you divert to the shower does any water run out of the spout? Back to you, Tom

Sometimes when I pull the water knob out all or most of the way and then pull up on the diverter , it shoots out the spout. I had replaced the spout about 2 years ago after I bought the house because of this problem.

Sounds like it's built up some minerals that's blocking the action. You can try soaking the spout in CRL or Lime Away but since they are so cheap why not simply replace the spout. Good luck, Tom