07 Transmission hard shift between 1st-2nd

About 6,000 miles ago, my 2nd Gen Prerunner started having issues with the transmission. There are currently 186k miles on the rig.
Between 1st and 2nd gear while driving is the issue. The RPM in first gear can almost run up to 5000rpm before shifting into 2nd gear, with a hard clunk being heard and you can really feel the hard shift.
I've been driving it similar to a stick- allowing the RPMs to come up to a normal range before letting off the gas and letting the truck shift into 2nd, and that seems to be working just fine for now, but I really want to fix the issue.
Last thing I want is a rebuild because of $$, so any suggestions would be appreciated.
I've been told it could be a solenoid, a fluid issue, my shitty driving, etc...
Thanks y'all.

 

any update on this?