My transmission wont shift it stays in first gear.

i take it is a automatic check gearbox transmission fluid or the torque converter may be at fault

The transmission control module is responsible for correct shifting of transmission.it is on side of tranny. the throttle position sensor takes all the necessary measurements and sends it over to the Electronic Control Module on transmission to make it shift, if its ok! Try by changing the shift module on transmission. If this will not work check or change the TPS and check for a bad wire also. Hope this helps you out! God-Bless!

there are only 3 issues here.
1 weak engine, , even 1st gear I have no engine power.
2: 1st revs normal but wont shift up.
3: the transmission slips. (flares) RPM goes nuts.

which one?

Check the transmission fluid and make sure it is both at the correct level and that it is not burnt smelling or brown. It should be a reddish color. A fluid flush and transmission filter change may be in order.

Check transmission fuse its the one labeled PRNDL or similar.Use a test light when you check it by the way.If the fuse is good then its probaly your ignition switch failed.If that fuse is bad or the ignition switch is not suppling power to that fuse your tack,speedo,and gear indicator wont work, and your transmission will go into a safe mode.Safe mode is just the transmission staying in 3rd gear all the time until you fix this.

Have you changed the fluid & filter lately? Start there, much cheaper fix than anything else.

either repair or replace the transmission...sounds like the sensor went out

just remove whatever you did to cause the problem... it probably messed with the electrical system and is interfering with the other things