Low Water Pressure to Shower only - Tub fine

I recently changed out the diverter to our delta shower faucet (push in the wall type). At first, water leaked out of the tub faucet and there was a noticable drop in water pressure to the shower. I originally bought a "universal" diverter and once the leak to the tub faucet was noticed, I returned it and replaced with a Delta original part diverter. That stopped the leak but did not resolve the water pressure issue. There is not a problem with the shower head being clogged as pressure is still low when the head is removed. It takes 3-4 seconds for water to find its way up the shower pipe when it used to be almost instantanous. All was fine until the plastic part of the original diverter broke which caused me to replace the diverter. Pressure to the tub and all other fixtures within the house seems to be normal. I am so confused as to why the low pressure. I just erected new tile on the walls around the tub and really don't want to tear into the wall unnecessarily. (so as not to confuse, all was well after the tile replacement, no plumbing alterations were done)

Could the little plastic part that broke off the diverter be causing blockage within the plumbing somewhere? If so, where? I'm open to any and all suggestions. I'm obviously not a plumber but otherwise pretty handy. This one stumps me!!!

I've not had any replies...I guess everyone is bumfuzzled like me.

It very possible that apeice of the old divirter is lodged in the faucet body.
Can you tell me the model# so can find a diagram?You might try taking it
apart.to see If any thing falls out.Also how old is the faucet?

I appreciate the reply from both.

I don't know the model # or age of the faucet. I just bought the house last year. It was built in the mid 80's. I'll try as suggested to disassemble to see if anything falls out. I didn't think that was possible but I don't have any better ideas.

Thanks again.

Sounds like a low flow mixer valve. Is that new also? Restricts the shower head line but not the tub line (otherwise it would take forever to fill the tub.)