04 Chevy Trailblazer losing power and over revving during gear changes

I've been doing work on my mother in laws trailblazer and she really loves
this truck but shes let it go down the drain and I'm trying to get it back to
where it should be, I had 5 codes pop on me but the ones I'm worried the
most about are P0172, P0894, P0526. I've looked up what they mean but i
need some tips on how to solve it without having to take it in and either lose
everything i own due to the bill or lose the truck entirely. The truck as soon
as you start it it starts chugging pretty bad goes from about 750rpm - around
1400rpm just sitting there, start driving and the chugging will almost rock you
back and forth and as you drive second gear will over rev trying to shift and
third gear will almost red line trying to shift but as long as you let off the gas
a little it will shift but if you turn on the truck and let it idle for more then 15-20
mins you will hear it sound like its about to take off like a rocket and you look
at the dash and its overheating to the extreme and you can hear the coolent
boiling under the hood. its due for an oil change any day now and im about
to go and change the spark plugs and im about to change tranny fluid and
filter again even though its a little early. Now this is a 04 Trailblazer LS 4.2l
and it does have 285,000+ miles on it, but is there anything thing i could do
to help whats going on please any advice would be awesome, Thanks
everyone.