2001 Impala 3.4L Weird Shifting

[Viperonic]

Hey Guys, recently I have been having some problems with my 2001 Impala which has 205k miles on it, Whenever I start it cold it seems like it is stuck in 3rd and sometimes 2nd when accelerating,like i could have the peddle to the metal and it would not be accelerating the best, when i do that the rpm's cut off at a certain point and then once i get to about 30 the rpm's start going up. Plus I am able to go to 1st gear occasionally after about 20min of driving it. shifting the shifter to gear one manually does not work at all.

Current Faults in my engine are:
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P0128 - Powertrain
Coolant Thermostat (Coolant temp below thermostat regulating temps)

P0336 Powertrain
Crankshaft Position Sensor A Circuit Range/Performance

P0404 - Powertrain
Exhaust Gas Recirculation Control Circuit Range/Performance
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I have replaced the crankshaft position sensor before and it did nothing and replacing the temp sensor for the thermostat did nothing as well. I have replaced my ECU and it did not fix the problem for either of those problems.

Thank you guys for your time in helping me thanks!

[Blue Bowtie]

The CTS needs to be addressed first. Without a reliable CTS signal the PCM will assume a -40° temperature and operate the engine in a very rich mode.

[maxwedge]

And it will not go into lock up.

[Tech II]

9 out of 10 times, P0128 is a thermostat.....