need help...

It sure seems like there has to be a clog somewhere. The impeller is a good place to start looking.

Though it won't make a lot of difference the 1½" piping would be much better than the 1¼". Since you've effectively changed all the piping (suction back to hose & discharge from 1½ to 1¼) I'd start looking at the pump and filter for the problem.
 
Just wanted to add that from previous experience that I've found the Intex impeller on my pump to get clogged up very easily with elm seeds that get sucked through the strainer baskets. I've even had several small sticks get lodged in there somehow! When that happened I had very low flow out the return. I'd have to disassemble the pump and clean out the impeller and then it was back in business as usual. So definitely see if the pump impeller has stuff lodged in it.
 
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