Hard Shift into 1st Gear

My 1999 Tacoma shifts fine into 1st gear and reverse when it's cold, but after it's fully warmed up the shift becomes difficult. All the other gears shift normally when it's warmed up. Any help would be much appreciated. Thanks!

 

Welcome to TW, this very commonly a clutch issue, fluids up, clutch all working OK? The clutch may be slightly engaging, causing difficulty in first but being a synchro, all other gears appear fine.

Had the same issue and it turns out I have a mystery leak. Haven't had a problem since.

 

Couple of things to try... shut the motor off and see if she slips into 1st then, if so, like the rocknbil said, there is a clutch/pilot bearing issue. The next thing is pull back slightly on the shifter like you want to engage 2nd gear, this will slow the gear stack and align the syncros and see if that helps.