Need help

I have a 2001 Chevy S10 4.3 LS 4WD. About 170-
180,000 miles. A few weeks ago I was going about
70 and lost power, it didn't stall, it just wouldn't
accelerate, the RPMs would climb but speed
wouldnt. The steering got really stiff and my
battery light came on. I couldn't get it to start
afterwards and was told it was the alternator and
got it replaced. After that, it still didn't seem quite
right, between 40 and 55 mph the RPMs would
jump around. Then it did the exact same thing to
me again when I was going 70. Except I got it to
start a while later. Now since this passed sunday,  
my RPMs would climb and climb and I would
loose speed and sometimes barley gain and it
wouldn't shift itslef. I took it to an autozone and
had them run codes. The EGR valve showed it was
a fault so we replaced it, nothing changed, I had
the codes ran again and the EGR valve had cleared
and it was showing multiple misfires and an
oxygen sensor. We removed the distributor cap
and it was a little coreoded, nothing serious but we
replaced it anyway along with the rotor. I drove it
and nothing changed. I had codes ran again and it
showed the oxygen sensor again, so I replaced it.
Again nothing changed, I had codes ran again and
no codes showed up anymore. The truck sounds
better running wise but, it still has no power. The
pedal can be to the floor and the rpms stay
between 1-2000, and it barlet barley creeps in
speed it won't go over 5mph. I don't know what to
do anymore.?