97 Mazda B4000 5-speed, 4WD.

I bought this truck used a year or so ago.  Purchased the extended
warranty with it.

After a couple of months I noticed that after driving the truck for
25-30 miles the transmission was almost impossible to shift into 1st or
2nd -- upshift or downshift -- there were times I had to shove on the
stick so hard I was afraid I was going to break the gearshift stick.
Double-clutching would help sometimes.

Took it to the dealer.  They replaced:  transmission, master and slave
cylinders, throwout bearing, clutch disk.

Now, it's doing the same thing but only in 2nd gear and not so bad as
before.  Drive 25-30 miles and it is very difficult to shift into 2nd
gear -- upshift and downshift -- double-clutching makes it shift fairly
smoothly.  Also, it seems that the longer I drive it, the more
difficult it becomes -- I drove 60 miles last week and it was very
difficult to get into 2nd, even with double-clutching.

All other shifting is smooth, including into first.

Any suggestions?

Thanks.