I have noticed recently that my truck (2003 F150 5.4L V8 Bi-Fuel, automatic) seems to be slow to shift. For example, if I am going 45 on an on ramp and try to accelerate to get onto the highway, there is sometimes a delay. Either I have to push the gas further, at which point it will quickly shift up and accelerate. Or I have to let off the gas and then try again, then it shifts normally, usually. Once I let off the gas, sometimes, I feel a jolt from the rear, I am assuming that is transmission shifting down quickly.

Any ideas what might cause something like that?