Am I using too much weight (workout)?

I workout in such a way where I alternate with like muscle groups (triceps and chest are worked on one day, biceps and back are worked on another, and repeat).

My goal is to train for strength, so I am using a lot of weight with 10 reps per set, 3 sets per machine..

I have noticed the following.
Assuming I first get to the gym I am able to lift 150 on the flag chest press. I then move to a tricep machine where I can do 90. I think move to the inclined chest press where I can lift 90 as well, and finally the pec fly machine where I can only lift 80 and barely complete the full set of three.

I seem to get fatigued as I get to the final machines of my workout.

I decided to try things in a different order and I noticed I could do the inclined chest press (normally 110) at 130 easily, but when it came time to do the flat chest press (normally 150), I could barely get up 130.

I am also having problems finishing my full amount of sets\reps on the later machines of my workout, in the begining I am a beast :).

Am I using too much weight? Too many reps per set?