I have a 93 cummins with an ATS diesel auto tranny it has less than 5000 miles on it and i just noticed that the top speed is 72mph i'm pretty sure i have 3:55 gears in it.It acts like it dont want to shift into overdrive and when i turn the overdrive off it still runs the same speed.Please Help!!!!!

 

stock ?

chances are your hitting the governor and it's defueling, mine would barely hit 75 if I pushed it with 4.10's i added the 3200 gov spring and i could go a bit higher. when i switched to 3.55 it could push to 100

 

Yeah idk drove it today and got up too 85 which is plenty for me.Do have a stock ve pump besides a fuel pin but have 6x16 injectors and stock lift pump wonder if thats the problem with it if its defueling sometimes.

 

honestly it sounds like it is not shifting into overdrive, it is defueling because the govener weights are doing their job with that stock gov spring, injectors wont have anything to do with your defueling(that i know of, correct me if im wrong). that all checks out, i have a 727 3 speed in mine, with 4.10 gears i maxed at 75 mph with the stock 2600(i beleive its 2600 anyone correct me if i am wrong) govener spring. i intalled a 3200 (366) spring with a modified throttle stop and i can turn 3400 rpm+(no rpm gauge but from what others say with a 366 sping and modded arm you should be able to spin 3700-3900 if you have the power) and i my gps now says i am doing 92 mph. this is all with the non overdrive trans. so your 93 with the a518 and 3.55 gears should be able to push over 100 or get mighty close (project rust bucket with a 727 and a gear vendors overdrive could do over 100 easily he stated)
another thing that could be holding you back i feel is your torque converter, 727's and a518's are non lock up and their factory stall speed is 1700-1750 rpm, as they get used and abused (the fins inside get tweaked/ fatigued) their stall speeds go up to about 2000, so if your converter is slipping away your rpm's then you wont be getting them to the wheels, hence stuck at your current top speed even though you have a overdrive transmission. when i went down to the 1500 stall converter i noticed a huge difference in my cruising rpm as well as my top speed and acceleration. hope this helps some. just ideas from a fellow bomber.

 

sounds like i need to get a 3200 spring im hoping its not my ats torque converter that and the whole tranny is ats but i guess good reliable products can go wrong.thanks guys