I got a rebuilt tranny from AAmco, has around 40,000 mls. on it, (all highway)& noticed lately that between 45 to 55 it starts bucking, anyone have any info. about this???

 

Could be a mis-fire you are feeling.. you sure it's trans related ?

 

I agree with Tech, sounds like a misfire

 

Seems like tranny is having trouble in the 45-55 mph. range, runs fine from start to 65-70mph.,when hitting traffic & slow down to 45-55,in this range it bucks,clunks til i hit the gas & go past 55mph.. What do you think???

 

I agree with Tech, sounds like a misfire

 

How many miles on those plugs and boots/springs , replace them all / Clean all contacts on coils.

 

We just told you what we think.. any DTC's ?

 

First mistake buying trans from Aamco not going to say anymore.

 

Seriously, how many miles on the spark plugs in this truck? Unknown? Replace them.

OK, you just replaced the transmission and it's not yet a proven commodity; but that doesn't mean that's what the issue is. Try to not get fixated, you can do it.

 

Search "bucking at 40mph" or "bucking at 50mph" or really bucking at any specific speed in this section of the forum and you find that 99% of the time it is a misfire not a trans problem. Not saying yours isn't trans but most people think its the trans and we get if fixed by clearing up misfires. I'm betting you also have misfires. Its very common for these engines to have misfires that are much more noticeable at a specific speed. I would start cheap and simple. Replace the boots and springs on the coils, clean the points of contact on the coils. This has fixed all my misfires for about $40. If that doesnt fix it then its probably time for new plugs, or at least some better diagnosis with live data to determine which cylinder is misfiring. If you do a quick search as I suggested you will see we know what were talking about and have fixed this very problem for many members on here.