Transmission slips/jerks after 30 mph and braking at 30 mph

have transmission checked

if engine speed remains constant then your transmission is slipping , guessing? 30 mph is when the 2 to 3 gear shift is occurring , Id let a transmission expert look at it

When you say it "jerks," this description could fit several actual symptoms. If by "jerks" you mean the engine misfires, it could be caused by the need for a major tune-up (including plug wires and distributor cap), or it could be a problem with fuel delivery, contaminated fuel, or defective components in the fuel system.
I assume the CHECK ENGINE light is on (and has probably been illuminated for some time now). Begin by doing a readout of the stored codes, and use the results to begin your diagnosis.
If by "jerks" you mean the transmission is slipping (engine revs but car slows down or doesn't accelerate), you have a transmission issue. If the transmission fluid and strainer/filter have not been replaced within the past 5 years or 50,000 miles, have a complete transmission service performed.
If by "jerks" you mean that the steering wheel wobbles or pulls, you have a problem with the front suspension.
If by "jerks" you mean that the car shudders or pulls when you apply the brakes, you need brake work.
I think I covered all of the "jerks." ;)

jerking can be from many things
1: brakes locked up. or bad.
2: engine jerks
3: transmission jerks.

sluggish, same,
find a shop any auto repair shop to tell you which of the 3 it is.
then post for help.

keep in mind, not one person here can drive your car. and see that.

The transmission is the cause

maybe stuck e brake. rear rotors warped, or maybe collapsed brake hose or hoses. could even be proportionate valve or abs box

Not sure if your indicating a definite transaxle issue
& only at 40 to 50mph
Drag the brake while still on the gas, see
if it goes away,then you got torque converter lock-up
issues (TTC), if not then you need to make it is not
something other than the transmission, otherwise
the trans is in trouble and may have to come out
& apart
Check drive axles & all motor & trans mounts, regardless
of the trans problem

How new are your tires and when was the last time for a front end aliment?That might be it.

hi,

usually the auto trans has a filter in the pan. if the filters clogged it cant get enough pressure to shift. i recommend a new filter and gasket. cork gaskets are way easier to install than rubber gaskets. coat the cork gasket with form-a- gasket, you dont have to use an extreme amount, just enough so the gasket sticks to the pan.

jm

Are the engine rpms climbing when its jerking forward? seems like it could be a Transmission torque converter problem.